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

Groups > linux.kernel > #1347872

Re: [RFC PATCH] drivers: ata: Read Rx water mark value from device-tree

Show all headers | View raw

On Wednesday 02 March 2016 09:05:49 Michal Simek wrote:
> On 2.3.2016 06:53, Anurag Kumar Vulisha wrote:
> >>>>>
> >>>>> I would probably make this dependent on the compatible string
> >>>>> instead, and have a table in the device driver that uses a
> >>>>> specific value for each variant of the device, but either way should be
> >> fine.
> >>>>>
> >>>>> Having a separate property is most appropriate if for each
> >>>>> hardware revision there is exactly one ideal value, while a table
> >>>>> in the driver makes more sense if this takes a bit of tuning and
> >>>>> the driver might choose to optimize it differently based on other
> >>>>> constraints, such as its own interrupt handler implementation.
> 
> that 0x40 is value choose based on testing that it is not causing any
> visible problem and this is used as default value in the driver
> (PTC_RX_WM_VAL - ahci_ceva.c)
> 
> Values which you can setup are in range 0x0 - 0x7f (7bits). It means
> hardware fifo size is probably 0x80.
> 
> And this dt/module parameter is IMHO just sw setting setup by user.
> It means I am not quite sure that this is DT parameter because it is
> just SW setting.
> I expect this range will be valid for all silicon revisions.
> If happen that any silicon revision can't setup certain level because of
> HW bug we can handle it via DT parameter or specific compatible string.
> But setting up watermark SW level via DT doesn't look correct to me.
> 
> Please let me know what you think.

Ok, thanks for the background. I think we should just leave it to be
set by the driver then. Please make sure that each SoC specific .dtsi
file has a unique "compatible" string for the device though, so that
the driver can later override it based on the specific variant if
that ends up being necessary for performance or bug-avoidance.

	Arnd

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

RE: [RFC PATCH] drivers: ata: Read Rx water mark value from  device-tree Anurag Kumar Vulisha <anurag.kumar.vulisha@xilinx.com> - 2016-02-23 07:20 +0100
  Re: [RFC PATCH] drivers: ata: Read Rx water mark value from device-tree Arnd Bergmann <arnd@arndb.de> - 2016-02-23 11:30 +0100
    RE: [RFC PATCH] drivers: ata: Read Rx water mark value from  device-tree Anurag Kumar Vulisha <anurag.kumar.vulisha@xilinx.com> - 2016-02-23 16:40 +0100
      Re: [RFC PATCH] drivers: ata: Read Rx water mark value from  device-tree Rob Herring <robh@kernel.org> - 2016-02-23 20:30 +0100
        RE: [RFC PATCH] drivers: ata: Read Rx water mark value from  device-tree Anurag Kumar Vulisha <anurag.kumar.vulisha@xilinx.com> - 2016-02-26 14:50 +0100
        RE: [RFC PATCH] drivers: ata: Read Rx water mark value from  device-tree Anurag Kumar Vulisha <anurag.kumar.vulisha@xilinx.com> - 2016-03-02 07:10 +0100
          Re: [RFC PATCH] drivers: ata: Read Rx water mark value from  device-tree Michal Simek <michal.simek@xilinx.com> - 2016-03-02 09:10 +0100
            Re: [RFC PATCH] drivers: ata: Read Rx water mark value from device-tree Arnd Bergmann <arnd@arndb.de> - 2016-03-02 10:20 +0100
              Re: [RFC PATCH] drivers: ata: Read Rx water mark value from  device-tree Michal Simek <michal.simek@xilinx.com> - 2016-03-02 10:30 +0100
                Re: [RFC PATCH] drivers: ata: Read Rx water mark value from device-tree Arnd Bergmann <arnd@arndb.de> - 2016-03-02 12:50 +0100
                Re: [RFC PATCH] drivers: ata: Read Rx water mark value from  device-tree Michal Simek <michal.simek@xilinx.com> - 2016-03-02 13:10 +0100

csiph-web