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Re: [PATCH 08/11] MTD: m25p80: Add option to limit SPI transfer size.

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On Wednesday, July 22, 2015 at 09:30:54 AM, Michal Suchanek wrote:
> On 22 July 2015 at 06:49, Vinod Koul <vinod.koul@intel.com> wrote:
> > On Tue, Jul 21, 2015 at 10:14:11AM +0200, Michal Suchanek wrote:
> >> > Or alternatively we could publish the limitations of the channel using
> >> > capabilities so SPI knows I have a dmaengine channel and it can
> >> > transfer max N length transfers so would be able to break rather than
> >> > guessing it or coding in DT. Yes it may come from DT but that should
> >> > be dmaengine driver rather than client driver :)
> >> > 
> >> > This can be done by dma_get_slave_caps(chan, &caps)
> >> > 
> >> > And we add max_length as one more parameter to existing set
> >> > 
> >> > Also all this could be handled in generic SPI-dmaengine layer so that
> >> > individual drivers don't have to code it in
> >> > 
> >> > Let me know if this idea is okay, I can push the dmaengine bits...
> >> 
> >> It would be ok if there was a fixed limit. However, the limit depends
> >> on SPI slave settings. Presumably for other buses using the dmaengine
> >> the limit would depend on the bus or slave settings as well. I do not
> >> see a sane way of passing this all the way to the dmaengine driver.
> > 
> > I don't see why this should be client (SPI) dependent. The max length
> > supported is a dmaengine constraint, typically flowing from max
> > blocks/length it can transfer. Know this limit can allow clients to split
> > transfers.
> 
> In practice on the board I have the maximum transfer length before it
> fails depends on SPI bus speed which is set up per slave. I did not
> try searching the space of possible settings thorougly and settled for
> a setting that gives reasonable speed and transfer length.

This looks more like a signal integrity issue though.

> However, if this was not tied to the particular slave setting picked
> in the current DT a formula would be needed that translates arbitrary
> client settings to transfer size limit and there would be need to
> somehow get the client settings to the formula in the dmaengine
> driver.
> 
> Thanks
> 
> Michal

Best regards,
Marek Vasut
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Re: [PATCH 08/11] MTD: m25p80: Add option to limit SPI transfer size. Marek Vasut <marex@denx.de> - 2015-07-22 09:40 +0200
  Re: [PATCH 08/11] MTD: m25p80: Add option to limit SPI transfer size. Michal Suchanek <hramrach@gmail.com> - 2015-07-22 09:50 +0200
    Re: [PATCH 08/11] MTD: m25p80: Add option to limit SPI transfer size. Marek Vasut <marex@denx.de> - 2015-07-22 10:00 +0200
      Re: [PATCH 08/11] MTD: m25p80: Add option to limit SPI transfer size. Michal Suchanek <hramrach@gmail.com> - 2015-07-22 10:20 +0200
        Re: [PATCH 08/11] MTD: m25p80: Add option to limit SPI transfer size. Marek Vasut <marex@denx.de> - 2015-07-22 10:30 +0200
          Re: [PATCH 08/11] MTD: m25p80: Add option to limit SPI transfer size. Michal Suchanek <hramrach@gmail.com> - 2015-07-22 10:40 +0200
            Re: [PATCH 08/11] MTD: m25p80: Add option to limit SPI transfer size. Michal Suchanek <hramrach@gmail.com> - 2015-07-23 19:10 +0200
              Re: [PATCH 08/11] MTD: m25p80: Add option to limit SPI transfer size. Marek Vasut <marex@denx.de> - 2015-07-24 11:20 +0200
                Re: [PATCH 08/11] MTD: m25p80: Add option to limit SPI transfer size. Michal Suchanek <hramrach@gmail.com> - 2015-07-24 13:30 +0200
                Re: [PATCH 08/11] MTD: m25p80: Add option to limit SPI transfer size. Michal Suchanek <hramrach@gmail.com> - 2015-07-27 11:50 +0200

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