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Re: [PATCH 0/4] Add DMA support for ti_am335x_adc driver

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  Re: [PATCH 0/4] Add DMA support for ti_am335x_adc driver Jonathan Cameron <jic23@kernel.org> - 2016-09-25 11:50 +0200
    Re: [PATCH 0/4] Add DMA support for ti_am335x_adc driver Mugunthan V N <mugunthanvnm@ti.com> - 2016-09-29 15:10 +0200
      Re: [PATCH 0/4] Add DMA support for ti_am335x_adc driver John Syne <john3909@gmail.com> - 2016-09-30 05:40 +0200

#1490864 — Re: [PATCH 0/4] Add DMA support for ti_am335x_adc driver

On 21/09/16 17:11, Mugunthan V N wrote:
> The ADC has a 64 work depth fifo length which holds the ADC data
> till the CPU reads. So when a user program needs a large ADC data
> to operate on, then it has to do multiple reads to get its
> buffer. Currently if the application asks for 4 samples per
> channel with all 8 channels are enabled, kernel can provide only
> 3 samples per channel when all 8 channels are enabled (logs at
> [1]). So with DMA support user can request for large number of
> samples at a time (logs at [2]).
> 
> Tested the patch on AM437x-gp-evm and AM335x Boneblack with the
> patch [3] to enable ADC and pushed a branch for testing [4]
> 
> [1] - http://pastebin.ubuntu.com/23211490/
> [2] - http://pastebin.ubuntu.com/23211492/
> [3] - http://pastebin.ubuntu.com/23211494/
> [4] - git://git.ti.com/~mugunthanvnm/ti-linux-kernel/linux.git iio-dma
Just curious.  How fast is the ADC sampling at in these?  Never that
obvious for this driver!

I'm also curious as to whether you started to hit the limits of the
kfifo based interface.  Might be worth considering adding alternative
support for the dma buffers interface which is obviously much lower
overhead.

Good to have this work prior to that as the kfifo stuff is somewhat
easier to use.

Jonathan
> 
> Mugunthan V N (4):
>   mfd: ti_am335x_tscadc: store physical address
>   drivers: iio: ti_am335x_adc: add dma support
>   ARM: dts: am33xx: add DMA properties for tscadc
>   ARM: dts: am4372: add DMA properties for tscadc
> 
>  arch/arm/boot/dts/am33xx.dtsi        |   2 +
>  arch/arm/boot/dts/am4372.dtsi        |   2 +
>  drivers/iio/adc/ti_am335x_adc.c      | 160 ++++++++++++++++++++++++++++++++++-
>  drivers/mfd/ti_am335x_tscadc.c       |   1 +
>  include/linux/mfd/ti_am335x_tscadc.h |   8 ++
>  5 files changed, 170 insertions(+), 3 deletions(-)
> 

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#1493447

On Sunday 25 September 2016 03:11 PM, Jonathan Cameron wrote:
> On 21/09/16 17:11, Mugunthan V N wrote:
>> > The ADC has a 64 work depth fifo length which holds the ADC data
>> > till the CPU reads. So when a user program needs a large ADC data
>> > to operate on, then it has to do multiple reads to get its
>> > buffer. Currently if the application asks for 4 samples per
>> > channel with all 8 channels are enabled, kernel can provide only
>> > 3 samples per channel when all 8 channels are enabled (logs at
>> > [1]). So with DMA support user can request for large number of
>> > samples at a time (logs at [2]).
>> > 
>> > Tested the patch on AM437x-gp-evm and AM335x Boneblack with the
>> > patch [3] to enable ADC and pushed a branch for testing [4]
>> > 
>> > [1] - http://pastebin.ubuntu.com/23211490/
>> > [2] - http://pastebin.ubuntu.com/23211492/
>> > [3] - http://pastebin.ubuntu.com/23211494/
>> > [4] - git://git.ti.com/~mugunthanvnm/ti-linux-kernel/linux.git iio-dma
> Just curious.  How fast is the ADC sampling at in these?  Never that
> obvious for this driver!
> 
> I'm also curious as to whether you started to hit the limits of the
> kfifo based interface.  Might be worth considering adding alternative
> support for the dma buffers interface which is obviously much lower
> overhead.
> 
> Good to have this work prior to that as the kfifo stuff is somewhat
> easier to use.

Currently ADC clock is 3MHz, which can produce a data rate of 225KBps
per channel with no open delay and no averaging of samples. So when all
8 Channels are enables the data rate will be 1.75MBps

ADC can be operated at 24MHz, which can generate a data rate of 28MBps
with all 8 channels enabled and no open delay and averaging, but our
target is to get 800K samples per second per channel which has a data
rate of 12.5MBps

I think with this data rate, DMA will be the best option to implement
without any data loss and less cpu overload to read the ADC samples.

Regards
Mugunthan V N

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#1493868

I applied your patches to the following kernel:

github.com/RobertCNelson/bb-kernel.git 
branch am33x-v4.8

Changing 
#define REG_DMAENABLE_CLEAR	0x038
to
#define REG_DMAENABLE_CLEAR	0x03C

Also applying the following DTS changes:

		target = <&tscadc>;
		__overlay__ {

			status = "okay";
			adc {
				ti,adc-channels = <0 1 2 3 4 5 6>;
				ti,chan-step-avg = <0x1 0x1 0x1 0x1 0x1 0x1 0x1>;
				ti,chan-step-opendelay = <0x0 0x0 0x0 0x0 0x0 0x0 0x0>;
				ti,chan-step-sampledelay = <0x0 0x0 0x0 0x0 0x0 0x0 0x0>;
			};
		};

Running on a BeagleBoneBlack, I was able to stream samples at 200ksps continuously and it looked stable. 

htop showed CPU utilization between 5% and 7%

Thank you for getting this to work.

Regards,
John




> On Sep 29, 2016, at 6:01 AM, Mugunthan V N <mugunthanvnm@ti.com> wrote:
> 
> On Sunday 25 September 2016 03:11 PM, Jonathan Cameron wrote:
>> On 21/09/16 17:11, Mugunthan V N wrote:
>>>> The ADC has a 64 work depth fifo length which holds the ADC data
>>>> till the CPU reads. So when a user program needs a large ADC data
>>>> to operate on, then it has to do multiple reads to get its
>>>> buffer. Currently if the application asks for 4 samples per
>>>> channel with all 8 channels are enabled, kernel can provide only
>>>> 3 samples per channel when all 8 channels are enabled (logs at
>>>> [1]). So with DMA support user can request for large number of
>>>> samples at a time (logs at [2]).
>>>> 
>>>> Tested the patch on AM437x-gp-evm and AM335x Boneblack with the
>>>> patch [3] to enable ADC and pushed a branch for testing [4]
>>>> 
>>>> [1] - http://pastebin.ubuntu.com/23211490/
>>>> [2] - http://pastebin.ubuntu.com/23211492/
>>>> [3] - http://pastebin.ubuntu.com/23211494/
>>>> [4] - git://git.ti.com/~mugunthanvnm/ti-linux-kernel/linux.git iio-dma
>> Just curious.  How fast is the ADC sampling at in these?  Never that
>> obvious for this driver!
>> 
>> I'm also curious as to whether you started to hit the limits of the
>> kfifo based interface.  Might be worth considering adding alternative
>> support for the dma buffers interface which is obviously much lower
>> overhead.
>> 
>> Good to have this work prior to that as the kfifo stuff is somewhat
>> easier to use.
> 
> Currently ADC clock is 3MHz, which can produce a data rate of 225KBps
> per channel with no open delay and no averaging of samples. So when all
> 8 Channels are enables the data rate will be 1.75MBps
> 
> ADC can be operated at 24MHz, which can generate a data rate of 28MBps
> with all 8 channels enabled and no open delay and averaging, but our
> target is to get 800K samples per second per channel which has a data
> rate of 12.5MBps
> 
> I think with this data rate, DMA will be the best option to implement
> without any data loss and less cpu overload to read the ADC samples.
> 
> Regards
> Mugunthan V N
> --
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