linux-kernel - Re: [PATCH 3/5] spi: sunxi: expose maximum transfer size limit

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Message-ID: <CAOMqctQdbipvvTnF253S4jGDos1crYXk9nuzDcRvy4geeS=GrQ@mail.gmail.com>
Date:	Mon, 30 May 2016 10:57:10 +0200
From:	Michal Suchanek <hramrach@...il.com>
To:	Maxime Ripard <maxime.ripard@...e-electrons.com>
Cc:	linux-sunxi <linux-sunxi@...glegroups.com>,
	Mark Brown <broonie@...nel.org>, Chen-Yu Tsai <wens@...e.org>,
	linux-spi <linux-spi@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/5] spi: sunxi: expose maximum transfer size limit

Hello,

On 30 May 2016 at 10:37, Maxime Ripard <maxime.ripard@...e-electrons.com> wrote:
> On Thu, May 26, 2016 at 07:25:24PM -0000, Michal Suchanek wrote:
>> The sun4i spi hardware can trasfer at most 63 bytes of data without DMA
>> support so report the limitation. Same on sun6i.
>
> Is it? Is there timeouts on the A31 and later SoCs?
>

I have no sun6i hardware to test with.

This is an advisory limit you can query and it better be smaller
rather than unreliable. The hard limit in the driver is still
SUN6I_FIFO_DEPTH (which is 128 bytes on sun6i).

You can test his without any actual SPI device. Unused pins you can
multiplex as SPI suffice.

Thanks

Michal