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Message-ID: <20151105152943.GP18409@sirena.org.uk>
Date: Thu, 5 Nov 2015 15:29:43 +0000
From: Mark Brown <broonie@...nel.org>
To: Vignesh R <vigneshr@...com>
Cc: Tony Lindgren <tony@...mide.com>,
Michal Suchanek <hramrach@...il.com>,
Russell King <linux@....linux.org.uk>,
devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-omap@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
linux-mtd@...ts.infradead.org, linux-spi@...r.kernel.org
Subject: Re: [PATCH v2 1/5] spi: introduce mmap read support for spi flash
devices
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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