linux-kernel - Re: [PATCH] sst25l.c: fix multi-part messages with broken spi masters

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Date:	Wed, 05 May 2010 08:45:49 +0300
From:	Artem Bityutskiy <dedekind1@...il.com>
To:	H Hartley Sweeten <hartleys@...ionengravers.com>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>,
	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
	"ryan@...ewatersys.com" <ryan@...ewatersys.com>,
	"andre@...ewatersys.com" <andre@...ewatersys.com>,
	David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH] sst25l.c: fix multi-part messages with broken spi
 masters

On Thu, 2010-04-29 at 13:34 -0500, H Hartley Sweeten wrote:
> Some SPI masters (ep93xx) have limitations when using the SFRMOUT
> signal for the spi device chip select.  The SFRMOUT signal is
> only asserted as long as the spi transmit fifo contains data.  As
> soon as the last bit is clocked into the receive fifo it gets
> deasserted.
> 
> The functions sst25l_status and sst25l_match_device use the API
> function spi_write_then_read to write a command to the flash then
> read the response back.  This API function creates a two part spi
> message for the write then read.  When this message is transferred
> the SFRMOUT signal ends up getting deasserted after the command
> phase.  This causes the command to get aborted by the device so
> the read phase returns invalid data.
> 
> By changing sst25l_status and sst25l_match_device to use a single
> transfer synchronous message, the SFRMOUT signal stays asserted
> during the entire message so the correct data always gets returned.
> 
> This change will have no effect on SPI masters which use a chip
> select mechanism (GPIO's, etc.) which does stay asserted correctly.
> As a bonus, the single transfer synchronous messages complete faster
> than multi-part messages.
> 
> Signed-off-by: H Hartley Sweeten <hsweeten@...ionengravers.com>
> Cc: David Woodhouse <dwmw2@...radead.org>
> Cc: Artem Bityutskiy <dedekind1@...il.com>
> Cc: Andre Renaud <andre@...ewatersys.com>
> Cc: Ryan Mallon <ryan@...ewatersys.com>

Pushed to l2-mtd-2.6 / dunno.

But please, notice for future:
1. It is much nicer to put something like [PATCH v2] when you re-send.
2. In MTD we prefix everything with mtd:

-- 
Best Regards,
Artem Bityutskiy (Артём Битюцкий)

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