linux-kernel - Re: [PATCH] spi: pxa2xx: Only claim CS GPIOs when the slave device is created

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Message-ID: <db94e41e-5772-ec74-8587-3192dc866040@web.de>
Date:   Mon, 24 Jul 2017 13:06:43 +0200
From:   Jan Kiszka <jan.kiszka@....de>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Daniel Mack <daniel@...que.org>,
        Haojian Zhuang <haojian.zhuang@...il.com>,
        Robert Jarzmik <robert.jarzmik@...e.fr>,
        Mark Brown <broonie@...nel.org>,
        linux-spi <linux-spi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] spi: pxa2xx: Only claim CS GPIOs when the slave device is
 created

On 2017-07-24 13:02, Andy Shevchenko wrote:
> On Mon, Jul 24, 2017 at 1:53 PM, Jan Kiszka <jan.kiszka@....de> wrote:
>> On 2017-07-24 12:44, Andy Shevchenko wrote:
>>> +Cc: Mika
>>>
>>> On Sat, Jul 8, 2017 at 11:41 AM, Jan Kiszka <jan.kiszka@....de> wrote:
>>>> From: Jan Kiszka <jan.kiszka@...mens.com>
>>>>
>>>> Avoid hogging chip select GPIOs just because they are listed for the
>>>> master. They might be mulitplexed and, if no slave device is attached,
>>>> used for different purposes. Moreover, this strategy avoids having to
>>>> allocate a cs_gpiods structure.
>>>>
>>>> Tested on the IOT2000 where the second SPI bus is connected to an
>>>> Arduino-compatible connector and multiplexed between SPI, GPIO and PWM
>>>> usage.
> 
>>> This breaks all systems which are using _DSD.
>>
>> Err, can you elaborate? Worked fine here with _DSD on the IOT2000.
> 
> Sure, the setup() function can be called several times for the same
> chip (as written in the comment inside the function).
> Definitely your code doesn't follow this, since gpiod_get_index() is
> returning -EBUSY when called 2+ time, that's what I got on all my
> tests.

Ah, multiple devices on the same controller - I only had one.

> 
>>> While I'm looking for fix, I get feeling that the approach itself is not right,
>>>
>>> So, for now I would vote for immediate revert and then rethink what we
>>> can do here.
>>
>> I'm fine with reverting because the patch wasn't clean anyway (mixed old
>> and new GPIO API) - aside from whatever you found in addition.
> 
>> I had an
>> update pending but, as you are looking into this anyway, I'm sure your
>> patches will be more holistic.
> 
> Please, send it as RFC, because it might have something we can use/re-use.
> 

OK, will dig them out later.

Jan



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