linux-kernel - Re: [PATCH v3 7/7] spi: imx: defer spi initialization, if DMA engine is pending

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Message-ID: <564706ED.70102@gmail.com>
Date:	Sat, 14 Nov 2015 11:03:25 +0100
From:	Anton Bondarenko <anton.bondarenko.sama@...il.com>
To:	Sascha Hauer <s.hauer@...gutronix.de>
Cc:	broonie@...nel.org, b38343@...escale.com,
	linux-kernel@...r.kernel.org, linux-spi@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	vladimir_zapolskiy@...tor.com, jiada_wang@...tor.com
Subject: Re: [PATCH v3 7/7] spi: imx: defer spi initialization, if DMA engine
 is pending



On 05.11.2015 17:18, Anton Bondarenko wrote:
> On 05.11.2015 09:59, Sascha Hauer wrote:
>> On Sun, Nov 01, 2015 at 03:41:41PM +0100, Anton Bondarenko wrote:
>>> From: Anton Bondarenko <anton_bondarenko@...tor.com>
>>>
>>> If SPI device supports DMA mode, but DMA controller is not yet
>>> available due to e.g. a delay in the corresponding kernel module
>>> initialization, retry to initialize SPI driver later on instead of
>>> falling back into PIO only mode.
>>>
>>> Signed-off-by: Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>
>>> Signed-off-by: Anton Bondarenko <anton_bondarenko@...tor.com>
>>
>> Ok, so 6/7 is only part of the deferral story. Maybe squash the two
>> patches into one?
>>
>> Sascha
>
> I would like to keep these two changes separately since I have a small
> concern about this exact change.
>
> Let's assume such scenario:
> - ECSPI configured to use DMA in device tree and DMA controller
> description specified. But there is no driver for this controller in
> kernel.
> In this case dmaengine will always return -EDEFER and driver postpone
> spi-imx initialization. So finally there will be no SPI support even in
> PIO mode.
> Or for example spi-imx will be compiled into kernel, but DMA controller
> driver will be on SPI-NOR based rootfs.
>
> So the question is "Should we allow user to use incorrect combination of
> kernel configuration and DTS and work at least with some limitation?" Or
> should we try to guarantee device tree file requirement to use DMA.
>
> Any thoughts?
>
> Regards, Anton

Does anyone has other comments regarding this commit?

Regards, Anton
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