Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1234936 > unrolled thread

Re: [PATCH v2 1/9] dmaengine: st_fdma: Add STMicroelectronics FDMA DT binding documentation

Back to article view | Back to linux.kernel

This discussion starts older than the indexed window; earlier articles aren't shown. The article labeled Started by below is the oldest one visible, not the original post.

Contents

  Re: [PATCH v2 1/9] dmaengine: st_fdma: Add STMicroelectronics FDMA  DT binding documentation Peter Griffin <peter.griffin@linaro.org> - 2015-09-29 12:10 +0200
    Re: [PATCH v2 1/9] dmaengine: st_fdma: Add STMicroelectronics FDMA DT binding documentation Arnd Bergmann <arnd@arndb.de> - 2015-09-29 13:20 +0200
      Re: [PATCH v2 1/9] dmaengine: st_fdma: Add STMicroelectronics FDMA  DT binding documentation Peter Griffin <peter.griffin@linaro.org> - 2015-09-29 14:20 +0200
        Re: [PATCH v2 1/9] dmaengine: st_fdma: Add STMicroelectronics FDMA DT binding documentation Arnd Bergmann <arnd@arndb.de> - 2015-09-29 14:40 +0200
          Re: [PATCH v2 1/9] dmaengine: st_fdma: Add STMicroelectronics FDMA  DT binding documentation Peter Griffin <peter.griffin@linaro.org> - 2015-09-29 15:50 +0200
            Re: [PATCH v2 1/9] dmaengine: st_fdma: Add STMicroelectronics FDMA DT binding documentation Arnd Bergmann <arnd@arndb.de> - 2015-09-29 16:20 +0200

#1234936 — Re: [PATCH v2 1/9] dmaengine: st_fdma: Add STMicroelectronics FDMA DT binding documentation

Hi Lee,

On Mon, 14 Sep 2015, Lee Jones wrote:

> > On Fri, 11 Sep 2015, Arnd Bergmann wrote:
> > 
> > > On Friday 11 September 2015 15:14:23 Peter Griffin wrote:
> > > > +- st,fdma-id	: Must contain fdma controller number
> > > 
> > > What for?
> > 
> > It is used by the driver to generate a unique firmware name.
> > Basically we need to know which controller instance we
> > are as each controller has a different firmware which needs
> > to be loaded.
> > 
> > Rob did say that having a index type property is undesirable
> > over here, see my reply at the bottom
> > http://www.spinics.net/lists/devicetree/msg92529.html.
> > 
> > However I can't think of any other useful properties we could add
> > to derive this information.
> 
> I wouldn't use a property at all.  Why not use the compatible string?
> 
> Who chooses the naming scheme of the firmware binary?

ST

> 
> Is there any reason they can't be:
> 
>   fdma_STiH407_audio.elf
>   fdma_STiH407_app.elf
>   fdma_STiH407_free_running.elf

Not sure, we could easily rename them locally. Getting ST to change
the firmware names in the stlinux distro might be harder.
My personal preference is to leave the firmware names "as is", unless
there is a real show stopper reason where we *have* to change them e.g.
we can't support all STi platforms with the same userspace because
the firmware filenames aren't unique enough.

> 
> Then you can have a different compatible for each:
> 
>   compatible = "st,stih407-fdma-mpe31-audio";
>   compatible = "st,stih407-fdma-mpe31-app";
>   compatible = "st,stih407-fdma-mpe31-free-running";

I think if you took the approach of only using the compatible
you would still need to use the fdma instance number
otherwise you end up with the same problems discussed in the 
"Firmware filename in DT" thread [1] e.g.

   compatible = "st,stih407-fdma-mpe31-0";
   compatible = "st,stih407-fdma-mpe31-1";
   compatible = "st,stih407-fdma-mpe31-2";

Specifically the problem is related to

"The hardware is identical, and different firmware is used to apply
   it in different ways."

Which is the case with fdma. By encoding the "way you wish to apply it" into the
compatible string, it causes problems if you want to change for example fdma0
to do some other function other than audio.

You then require a DT update, (when the hardware hasn't changed, just the
firmware) which is the same problem as using the filename directly in DT.

Therefore I believe it is important that the DT binding does *not* encode the
way the hardware is to be applied into the binding in *any* way, and defers this
 decision to the driver.
That is the rationale / reasoning behind choosing the fdma instance number.

Assuming you agree with my arguments above, then the choice becomes between 
having a fdma instance DT property, or having lots of compatibles where the only
difference is the appending of the instance number. I think out of the two I prefer
my original approach.

Any thoughts from the DT folks?

regards,

Peter.

[1] http://comments.gmane.org/gmane.linux.drivers.devicetree/133782
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [next] | [standalone]

#1234976 — Re: [PATCH v2 1/9] dmaengine: st_fdma: Add STMicroelectronics FDMA DT binding documentation

On Tuesday 29 September 2015 11:04:40 Peter Griffin wrote:
> 
> "The hardware is identical, and different firmware is used to apply
>    it in different ways."
> 
> Which is the case with fdma. By encoding the "way you wish to apply it" into the
> compatible string, it causes problems if you want to change for example fdma0
> to do some other function other than audio.
> 
> You then require a DT update, (when the hardware hasn't changed, just the
> firmware) which is the same problem as using the filename directly in DT.
> 
> Therefore I believe it is important that the DT binding does *not* encode the
> way the hardware is to be applied into the binding in *any* way, and defers this
>  decision to the driver.
> That is the rationale / reasoning behind choosing the fdma instance number.
> 
> Assuming you agree with my arguments above, then the choice becomes between 
> having a fdma instance DT property, or having lots of compatibles where the only
> difference is the appending of the instance number. I think out of the two I prefer
> my original approach.
> 
> Any thoughts from the DT folks?

To me both approaches sound wrong: basing the firmware name on the instance
number requires that each instance is always used in the same way, which
is not guaranteed to be the case, and you correctly describe the problem with
using the compatible string for the firmware name if the driver for the FDMA
does not actually care what firmware is being used here.

Whatever code makes the decision as to how the FDMA is used should also
decide on the name of the firmware file. You can have a mapping in the
driver that contains the file names that are used by ST's distro, possibly
with a fallback mechanism that tries more meaningful names first.

	Arnd
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [prev] | [next] | [standalone]

#1235014

Hi Arnd,

On Tue, 29 Sep 2015, Arnd Bergmann wrote:

> On Tuesday 29 September 2015 11:04:40 Peter Griffin wrote:
> > 
> > "The hardware is identical, and different firmware is used to apply
> >    it in different ways."
> > 
> > Which is the case with fdma. By encoding the "way you wish to apply it" into the
> > compatible string, it causes problems if you want to change for example fdma0
> > to do some other function other than audio.
> > 
> > You then require a DT update, (when the hardware hasn't changed, just the
> > firmware) which is the same problem as using the filename directly in DT.
> > 
> > Therefore I believe it is important that the DT binding does *not* encode the
> > way the hardware is to be applied into the binding in *any* way, and defers this
> >  decision to the driver.
> > That is the rationale / reasoning behind choosing the fdma instance number.
> > 
> > Assuming you agree with my arguments above, then the choice becomes between 
> > having a fdma instance DT property, or having lots of compatibles where the only
> > difference is the appending of the instance number. I think out of the two I prefer
> > my original approach.
> > 
> > Any thoughts from the DT folks?
> 
> To me both approaches sound wrong: basing the firmware name on the instance
> number requires that each instance is always used in the same way, which
> is not guaranteed to be the case,

Does it? I didn't think it did.

Using the instance number as a DT property defers the decision over what firmware to
load to the driver, which can choose whatever firmware name it wishes.

e.g. in v4.3 it could load xyz.elf, in v4.4 it could choose abc.elf. The DT will remain
unchanged, but the use of that fdma instance has changed.

We currently only have one firmware for each instance with the "use" compiled into it.
If in the future we had two firmwares with different "uses" for the same instance some extra
logic would be required in the driver to make a decision on which firmware to load.

> and you correctly describe the problem with
> using the compatible string for the firmware name if the driver for the FDMA
> does not actually care what firmware is being used here.
> 
> Whatever code makes the decision as to how the FDMA is used should also
> decide on the name of the firmware file.

The code which makes this decision currently is the st_fdma.c driver. However it does
need to know which fdma controller it is operating on to make this decision correctly.

Apart from passing the fdma instance number in DT, how else can we determine which
controller we are?

I guess we could infer it by having a table in the driver containing the base addresses
of the controllers for a given SoC, and match that against what DT passes us in the
reg property. But that seems ugly, and is encoding the same information in two
different places.

I'm open to suggestions if there is a better way to do this.

regards,

Peter.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [prev] | [next] | [standalone]

#1235025 — Re: [PATCH v2 1/9] dmaengine: st_fdma: Add STMicroelectronics FDMA DT binding documentation

On Tuesday 29 September 2015 13:11:55 Peter Griffin wrote:
> Hi Arnd,
> 
> On Tue, 29 Sep 2015, Arnd Bergmann wrote:
> 
> > On Tuesday 29 September 2015 11:04:40 Peter Griffin wrote:
> > > 
> > > "The hardware is identical, and different firmware is used to apply
> > >    it in different ways."
> > > 
> > > Which is the case with fdma. By encoding the "way you wish to apply it" into the
> > > compatible string, it causes problems if you want to change for example fdma0
> > > to do some other function other than audio.
> > > 
> > > You then require a DT update, (when the hardware hasn't changed, just the
> > > firmware) which is the same problem as using the filename directly in DT.
> > > 
> > > Therefore I believe it is important that the DT binding does *not* encode the
> > > way the hardware is to be applied into the binding in *any* way, and defers this
> > >  decision to the driver.
> > > That is the rationale / reasoning behind choosing the fdma instance number.
> > > 
> > > Assuming you agree with my arguments above, then the choice becomes between 
> > > having a fdma instance DT property, or having lots of compatibles where the only
> > > difference is the appending of the instance number. I think out of the two I prefer
> > > my original approach.
> > > 
> > > Any thoughts from the DT folks?
> > 
> > To me both approaches sound wrong: basing the firmware name on the instance
> > number requires that each instance is always used in the same way, which
> > is not guaranteed to be the case,
> 
> Does it? I didn't think it did.
> 
> Using the instance number as a DT property defers the decision over what firmware to
> load to the driver, which can choose whatever firmware name it wishes.
> 
> e.g. in v4.3 it could load xyz.elf, in v4.4 it could choose abc.elf. The DT will remain
> unchanged, but the use of that fdma instance has changed.
> 
> We currently only have one firmware for each instance with the "use" compiled into it.
> If in the future we had two firmwares with different "uses" for the same instance some extra
> logic would be required in the driver to make a decision on which firmware to load.

Ok, I probably need some more background about what the firmware on this
device does, and what it could do with a different firmware. Could you
elaborate?

> > and you correctly describe the problem with
> > using the compatible string for the firmware name if the driver for the FDMA
> > does not actually care what firmware is being used here.
> > 
> > Whatever code makes the decision as to how the FDMA is used should also
> > decide on the name of the firmware file.
> 
> The code which makes this decision currently is the st_fdma.c driver. However it does
> need to know which fdma controller it is operating on to make this decision correctly.
> 
> Apart from passing the fdma instance number in DT, how else can we determine which
> controller we are?
> 
> I guess we could infer it by having a table in the driver containing the base addresses
> of the controllers for a given SoC, and match that against what DT passes us in the
> reg property. But that seems ugly, and is encoding the same information in two
> different places.
> 
> I'm open to suggestions if there is a better way to do this.

Using the address would be the same thing, that doesn't change the
fundamental logic. Can you explain why it matters which instance
a firmware is used on for this driver?

	Arnd
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [prev] | [next] | [standalone]

#1235081

Hi Arnd,

On Tue, 29 Sep 2015, Arnd Bergmann wrote:

> On Tuesday 29 September 2015 13:11:55 Peter Griffin wrote:
> > Hi Arnd,
> > 
> > On Tue, 29 Sep 2015, Arnd Bergmann wrote:
> > 
> > > On Tuesday 29 September 2015 11:04:40 Peter Griffin wrote:
> > > > 
> > > > "The hardware is identical, and different firmware is used to apply
> > > >    it in different ways."
> > > > 
> > > > Which is the case with fdma. By encoding the "way you wish to apply it" into the
> > > > compatible string, it causes problems if you want to change for example fdma0
> > > > to do some other function other than audio.
> > > > 
> > > > You then require a DT update, (when the hardware hasn't changed, just the
> > > > firmware) which is the same problem as using the filename directly in DT.
> > > > 
> > > > Therefore I believe it is important that the DT binding does *not* encode the
> > > > way the hardware is to be applied into the binding in *any* way, and defers this
> > > >  decision to the driver.
> > > > That is the rationale / reasoning behind choosing the fdma instance number.
> > > > 
> > > > Assuming you agree with my arguments above, then the choice becomes between 
> > > > having a fdma instance DT property, or having lots of compatibles where the only
> > > > difference is the appending of the instance number. I think out of the two I prefer
> > > > my original approach.
> > > > 
> > > > Any thoughts from the DT folks?
> > > 
> > > To me both approaches sound wrong: basing the firmware name on the instance
> > > number requires that each instance is always used in the same way, which
> > > is not guaranteed to be the case,
> > 
> > Does it? I didn't think it did.
> > 
> > Using the instance number as a DT property defers the decision over what firmware to
> > load to the driver, which can choose whatever firmware name it wishes.
> > 
> > e.g. in v4.3 it could load xyz.elf, in v4.4 it could choose abc.elf. The DT will remain
> > unchanged, but the use of that fdma instance has changed.
> > 
> > We currently only have one firmware for each instance with the "use" compiled into it.
> > If in the future we had two firmwares with different "uses" for the same instance some extra
> > logic would be required in the driver to make a decision on which firmware to load.
> 
> Ok, I probably need some more background about what the firmware on this
> device does, and what it could do with a different firmware. Could you
> elaborate?

So the fdma hw is a dma engine based around a xp70 slim core. It supports: -
* block memory move between 2 system locations
* paced transfer from system memory to paced peripheral
* paced transfer from a paced peripheral to system memory

I believe each firmware for each instance supports those 3 things.

However the xp70 also has some ancilary HW to facilitate Start Code Detection.
It is this feature which I believe would require a different firmware if we wanted to make
use of it. Looking at the functional spec each xp70 also
has 16 gp output signals which we could also control from the firmware. Whether
these are actually connected to anything useful inside the SoC I don't know.

> > > and you correctly describe the problem with
> > > using the compatible string for the firmware name if the driver for the FDMA
> > > does not actually care what firmware is being used here.
> > > 
> > > Whatever code makes the decision as to how the FDMA is used should also
> > > decide on the name of the firmware file.
> > 
> > The code which makes this decision currently is the st_fdma.c driver. However it does
> > need to know which fdma controller it is operating on to make this decision correctly.
> > 
> > Apart from passing the fdma instance number in DT, how else can we determine which
> > controller we are?
> > 
> > I guess we could infer it by having a table in the driver containing the base addresses
> > of the controllers for a given SoC, and match that against what DT passes us in the
> > reg property. But that seems ugly, and is encoding the same information in two
> > different places.
> > 
> > I'm open to suggestions if there is a better way to do this.
> 
> Using the address would be the same thing, that doesn't change the
> fundamental logic. Can you explain why it matters which instance
> a firmware is used on for this driver?

The reason we care, is that each instance has its own firmware file.

I just did a hexdump on the 3 different firmwares and compared them. Although the majority
of the binary is the same, there are various bytes which change at several different offsets
in the firmware file depending on the instance.

I don't have a xp70 toolchain or know enough about the cpu architecture to analyze what exactly
the firmware is doing at these locations.

regards,

Peter.


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [prev] | [next] | [standalone]

#1235144 — Re: [PATCH v2 1/9] dmaengine: st_fdma: Add STMicroelectronics FDMA DT binding documentation

On Tuesday 29 September 2015 14:42:15 Peter Griffin wrote:
> On Tue, 29 Sep 2015, Arnd Bergmann wrote:
> > On Tuesday 29 September 2015 13:11:55 Peter Griffin wrote:
> > > Does it? I didn't think it did.
> > > 
> > > Using the instance number as a DT property defers the decision over what firmware to
> > > load to the driver, which can choose whatever firmware name it wishes.
> > > 
> > > e.g. in v4.3 it could load xyz.elf, in v4.4 it could choose abc.elf. The DT will remain
> > > unchanged, but the use of that fdma instance has changed.
> > > 
> > > We currently only have one firmware for each instance with the "use" compiled into it.
> > > If in the future we had two firmwares with different "uses" for the same instance some extra
> > > logic would be required in the driver to make a decision on which firmware to load.
> > 
> > Ok, I probably need some more background about what the firmware on this
> > device does, and what it could do with a different firmware. Could you
> > elaborate?
> 
> So the fdma hw is a dma engine based around a xp70 slim core. It supports: -
> * block memory move between 2 system locations
> * paced transfer from system memory to paced peripheral
> * paced transfer from a paced peripheral to system memory
> 
> I believe each firmware for each instance supports those 3 things.

Ok

> However the xp70 also has some ancilary HW to facilitate Start Code Detection.
> It is this feature which I believe would require a different firmware if we wanted to make
> use of it. Looking at the functional spec each xp70 also
> has 16 gp output signals which we could also control from the firmware. Whether
> these are actually connected to anything useful inside the SoC I don't know.

I still don't understand what Start Code Detection is here.

> > > > and you correctly describe the problem with
> > > > using the compatible string for the firmware name if the driver for the FDMA
> > > > does not actually care what firmware is being used here.
> > > > 
> > > > Whatever code makes the decision as to how the FDMA is used should also
> > > > decide on the name of the firmware file.
> > > 
> > > The code which makes this decision currently is the st_fdma.c driver. However it does
> > > need to know which fdma controller it is operating on to make this decision correctly.
> > > 
> > > Apart from passing the fdma instance number in DT, how else can we determine which
> > > controller we are?
> > > 
> > > I guess we could infer it by having a table in the driver containing the base addresses
> > > of the controllers for a given SoC, and match that against what DT passes us in the
> > > reg property. But that seems ugly, and is encoding the same information in two
> > > different places.
> > > 
> > > I'm open to suggestions if there is a better way to do this.
> > 
> > Using the address would be the same thing, that doesn't change the
> > fundamental logic. Can you explain why it matters which instance
> > a firmware is used on for this driver?
> 
> The reason we care, is that each instance has its own firmware file.
> 
> I just did a hexdump on the 3 different firmwares and compared them. Although the majority
> of the binary is the same, there are various bytes which change at several different offsets
> in the firmware file depending on the instance.
> 
> I don't have a xp70 toolchain or know enough about the cpu architecture to analyze what exactly
> the firmware is doing at these locations.

This sounds like we should indeed treat them as different things: We don't
know what the difference is, but we know that each of them needs a different
firmware, and presumably if you get a new SoC variant, it will in turn
need three new ones.

In this case, I'd say using the compatible string to identify them is best,
using whatever the SoC documentation uses to describe them. You can use the
of_device_id data fields to look up the firmware name then.

If the output signals end up being connected to something we want to
control through the firmware, that also makes sense for a new compatible
string, as the driver needs to know about the feature in order to
communicate with the firmware, and the DT needs to be able to describe
the pins (e.g. by making the node act as a GPIO controller) in a way that
requires a different string, too.

	Arnd
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [prev] | [standalone]

Back to top | Article view | linux.kernel

csiph-web