Re: [PATCH v2 1/5] spi: introduce mmap read support for spi flash devices

From	Mark Brown <broonie@kernel.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH v2 1/5] spi: introduce mmap read support for spi flash devices
Date	2015-11-05 16:40 +0100
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On Thu, Nov 05, 2015 at 05:59:36PM +0530, Vignesh R wrote:
> On 11/04/2015 08:09 PM, Mark Brown wrote:

> > It's a bit worrying that this doesn't sync with the message queue except
> > via the mutex: this means that we might be out of order with respect to
> > any asynchronous transfers that are happening on the device.  I'm not
> > sure that this is a practical problem, though there is some risk of
> > unfair scheduling that would have to be under extreme load and it might
> > make sense to prioritise reads anyway.

> Since mmap interface is used only by mtd flash drivers and since almost
> all mtd flash devices use synchronous transfers (spi_sync()), IMO, there
> wont be out of order problem wrt mtd flashes.
> But mmap read might delay transfers queued for non mtd flash devices. It
> is difficult to wait for all transfers already queued to be pumped out
> by __spi_pump_messages() and then do the mmap transfer. Do you have any
> thoughts on how to sync with message queue?

Like I say I think it probably doesn't matter.  The main issue would be
with other devices sharing the bus with a flash chip.

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[PATCH v2 1/5] spi: introduce mmap read support for spi flash devices Vignesh R <vigneshr@ti.com> - 2015-11-03 11:10 +0100
  Re: [PATCH v2 1/5] spi: introduce mmap read support for spi flash devices Michal Suchanek <hramrach@gmail.com> - 2015-11-03 12:30 +0100
    Re: [PATCH v2 1/5] spi: introduce mmap read support for spi flash  devices Vignesh R <vigneshr@ti.com> - 2015-11-04 05:50 +0100
  Re: [PATCH v2 1/5] spi: introduce mmap read support for spi flash  devices Mark Brown <broonie@kernel.org> - 2015-11-04 15:50 +0100
    Re: [PATCH v2 1/5] spi: introduce mmap read support for spi flash  devices Vignesh R <vigneshr@ti.com> - 2015-11-05 13:40 +0100
      Re: [PATCH v2 1/5] spi: introduce mmap read support for spi flash  devices Mark Brown <broonie@kernel.org> - 2015-11-05 16:40 +0100

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