linux-kernel - Re: [PATCH] spi: Fix error code checking in spi_mem_exec

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Date: Wed, 13 Mar 2024 20:29:05 +0100
From: Pratyush Yadav <pratyush@...nel.org>
To: Florian Fainelli <florian.fainelli@...adcom.com>
Cc: Pratyush Yadav <pratyush@...nel.org>,  Michael Walle
 <mwalle@...nel.org>,  linux-spi@...r.kernel.org,  Mark Brown
 <broonie@...nel.org>,  Miquel Raynal <miquel.raynal@...tlin.com>,  Mika
 Westerberg <mika.westerberg@...ux.intel.com>,  "Chia-Lin Kao (AceLan)"
 <acelan.kao@...onical.com>,  open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] spi: Fix error code checking in spi_mem_exec_op()

On Wed, Mar 13 2024, Florian Fainelli wrote:

> On 3/13/24 11:28, Pratyush Yadav wrote:
>> On Wed, Mar 13 2024, Michael Walle wrote:
>>
>>> On Wed Mar 13, 2024 at 6:10 PM CET, Florian Fainelli wrote:
>>>> After commit cff49d58f57e ("spi: Unify error codes by replacing -ENOTSUPP with
>>>> -EOPNOTSUPP"), our SPI NOR flashes would stop probing with the following
>>>> visible in the kernel log:
>>>>
>>>> [    2.196300] brcmstb_qspi f0440920.qspi: using bspi-mspi mode
>>>> [    2.210295] spi-nor: probe of spi1.0 failed with error -95
>>>>
>>>> It turns out that the check in spi_mem_exec_op() was changed to check
>>>> for -ENOTSUPP (old error code) or -EOPNOTSUPP (new error code), but this
>>>> means that for drivers that were converted, the second condition is now
>>>> true, and we stop falling through like we used to. Fix the error to
>>>> check for neither error being neither -ENOTSUPP *nor* -EOPNOTSUPP.
>>>>
>>>> Fixes: cff49d58f57e ("spi: Unify error codes by replacing -ENOTSUPP with -EOPNOTSUPP")
>>>> Signed-off-by: Florian Fainelli <florian.fainelli@...adcom.com>
>>>> Change-Id: I4159811f6c582c4de2143382473d2000b8755872
>>>
>>> Ha, thank you!
>>>
>>> Reviewed-by: Michael Walle <mwalle@...nel.org>
>>>
>>> FWIW in next, there is commit
>>> e63aef9c9121e ("spi: spi-mem: add statistics support to ->exec_op() calls")
>>> that probably will conflict with this one.
>>>
>>> Also, - not for this patch - but with that logic, spi_mem_exec_op()
>>> might return EOPNOTSUPP *or* ENOTSUPP, even for drivers which might
>>> still return ENOTSUPP, because there is one condition in
>>> spi_mem_exec_op() which will always return EOPNOTSUPP. That is
>>> somewhat confusing, no?
>> I agree. I suppose it would be better to do:
>>      if (!ret)
>>         return 0;
>>      if (ret == -ENOTSUPP || ret == -EOPNOTSUPP)
>>         return -EOPNOTSUPP;
>>
>
> But with e63aef9c9121e ("spi: spi-mem: add statistics support to ->exec_op()
> calls") applied, would not that mean duplicating the statistics gathering, or
> were the statistics gathering only intended for when ret == 0?

Hmm, I didn't properly understand this. Ignore my suggestion. Your patch
does the right thing.

In this case we should return ret when:

    ret is 0
    OR
    when ret is not -EOPNOTSUPP or -ENOTSUPP.

So if we get either of the two we _won't_ return and continue forward.

>From looking at just this, spi_mem_exec_op() only returns -EOPNOTSUPP so
far since it has:

	if (!spi_mem_internal_supports_op(mem, op))
		return -EOPNOTSUPP;

But then looking further, it has:

	ret = spi_sync(mem->spi, &msg);

	if (ret)
		return ret;

spi_sync() can return -ENOTSUPP if it goes via __spi_async(). I suppose
we would need to fix that if we want consistent return codes. But that
isn't a problem this patch should fix. So with the merge conflict fixed
up,

Reviewed-by: Pratyush Yadav <pratyush@...nel.org>

-- 
Regards,
Pratyush Yadav