linux-kernel - Re: [PATCH v3 3/6] spi: sun6i: restrict transfer length in PIO-mode

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Date:   Mon, 9 Apr 2018 12:27:03 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Sergey Suloev <ssuloev@...altech.com>
Cc:     Maxime Ripard <maxime.ripard@...tlin.com>,
        Chen-Yu Tsai <wens@...e.org>, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-spi@...r.kernel.org
Subject: Re: [PATCH v3 3/6] spi: sun6i: restrict transfer length in PIO-mode

On Mon, Apr 09, 2018 at 02:10:40PM +0300, Sergey Suloev wrote:
> On 04/09/2018 01:50 PM, Mark Brown wrote:
> > On Mon, Apr 09, 2018 at 01:26:23PM +0300, Sergey Suloev wrote:

> > > Because current implementation tries to send more than FIFO-depth of data in
> > > a single call to "transfer_one" which is wrong.

> > No, that's absolutely not the case.  All any of these functions has to
> > do is transfer whatever they were asked to, how they do it is not at all
> > important to the framework.

> I think you don't fully understand the issue. Let's talk about sun4i and 
> sun6i SPI  drivers separately.

> sun4i

> 1)it is correctly declaring max_transfer_size=FIFO depth for PIO mode  but
> transfer_one() function doesn't follow the declaration allowing PIO
> transfers longer than FIFO depth  by just refilling FIFO using 3/4 FIFO
> empty interrupt. I can definitely state here that long transfers WON'T WORK
> on real hardware. I tested it and that's why I can say that. But as soon as
> sun4i SPI driver  is correctly declaring max_transfer_size then "smart"
> clients will work well by limiting a single transfer size to FIFO depth. I
> tested it with real hardware, again.

None of this is in the slightest bit related to the use of transfer_one() 
vs transfer_one_message().  These are all implementation details and
will so far as I can tell apply equally to both APIs.

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