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SubjectRe: [PATCH] mfd: stm32-timers: Use dma_request_chan() instead dma_request_slave_channel()
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On 12/20/19 12:36 PM, Peter Ujfalusi wrote:
> Hi Fabrice,
>
> On 20/12/2019 10.54, Fabrice Gasnier wrote:
>> On 12/17/19 11:52 AM, Peter Ujfalusi wrote:
>>> dma_request_slave_channel() is a wrapper on top of dma_request_chan()
>>> eating up the error code.
>>>
>>> By using dma_request_chan() directly the driver can support deferred
>>> probing against DMA.
>>>
>>> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
>>> ---
>>> drivers/mfd/stm32-timers.c | 31 ++++++++++++++++++++++---------
>>> 1 file changed, 22 insertions(+), 9 deletions(-)
>>>
>>> diff --git a/drivers/mfd/stm32-timers.c b/drivers/mfd/stm32-timers.c
>>> index efcd4b980c94..34747e8a4a40 100644
>>> --- a/drivers/mfd/stm32-timers.c
>>> +++ b/drivers/mfd/stm32-timers.c
>>> @@ -167,10 +167,11 @@ static void stm32_timers_get_arr_size(struct stm32_timers *ddata)
>>> regmap_write(ddata->regmap, TIM_ARR, 0x0);
>>> }
>>>
>>> -static void stm32_timers_dma_probe(struct device *dev,
>>> +static int stm32_timers_dma_probe(struct device *dev,
>>> struct stm32_timers *ddata)
>>> {
>>> int i;
>>> + int ret = 0;
>>> char name[4];
>>>
>>> init_completion(&ddata->dma.completion);
>>> @@ -179,14 +180,22 @@ static void stm32_timers_dma_probe(struct device *dev,
>>> /* Optional DMA support: get valid DMA channel(s) or NULL */
>>> for (i = STM32_TIMERS_DMA_CH1; i <= STM32_TIMERS_DMA_CH4; i++) {
>>> snprintf(name, ARRAY_SIZE(name), "ch%1d", i + 1);
>>> - ddata->dma.chans[i] = dma_request_slave_channel(dev, name);
>>> + ddata->dma.chans[i] = dma_request_chan(dev, name);
>>> }
>>> - ddata->dma.chans[STM32_TIMERS_DMA_UP] =
>>> - dma_request_slave_channel(dev, "up");
>>> - ddata->dma.chans[STM32_TIMERS_DMA_TRIG] =
>>> - dma_request_slave_channel(dev, "trig");
>>> - ddata->dma.chans[STM32_TIMERS_DMA_COM] =
>>> - dma_request_slave_channel(dev, "com");
>>> + ddata->dma.chans[STM32_TIMERS_DMA_UP] = dma_request_chan(dev, "up");
>>> + ddata->dma.chans[STM32_TIMERS_DMA_TRIG] = dma_request_chan(dev, "trig");
>>> + ddata->dma.chans[STM32_TIMERS_DMA_COM] = dma_request_chan(dev, "com");
>>> +
>>> + for (i = STM32_TIMERS_DMA_CH1; i < STM32_TIMERS_MAX_DMAS; i++) {
>>> + if (IS_ERR(ddata->dma.chans[i])) {
>>> + if (PTR_ERR(ddata->dma.chans[i]) == -EPROBE_DEFER)> + ret = -EPROBE_DEFER;
>>
>> Hi Peter,
>>
>> Thanks for the patch,
>>
>> As the DMA is optional, I'd rather prefer to check explicitly there's no
>> device, and return any other error case, basically:
>>
>> if (PTR_ERR(ddata->dma.chans[i]) != -ENODEV)
>> return PTR_ERR(ddata->dma.chans[i]);
>
> My intention was to specifically pick and handle EPROBE_DEFER while not
> changing how the driver handles other errors, whether it because there
> is no DMA channel specified or there is a failure to get the channel.
>
> But if you prefer to ignore only ENODEV and report other errors then I
> can send v2.

Hi Peter,

Sorry for the late answer.

Yes, I'd prefer this please, not to hide other error case (as detailed
in other thread: https://lkml.org/lkml/2020/1/6/209). The only expected
"normal" error here is -ENODEV, as the DMA is optional.

> It could expose otherwise ignored configuration error (from DT?) and the
> change in the driver will be blamed for the regression.

I can do some testing at my end if needed, but I don't expect regression
here.

Thanks,
Fabrice

>
> Would it make sense to add the change you suggested as an iteration on
> top of this patch?
>
>>
>>> +
>>> + ddata->dma.chans[i] = NULL;
>>> + }
>>> + }
>>> +
>>> + return ret;
>>
>> With that, return 0 here.
>>
>>> }
>>>
>>> static void stm32_timers_dma_remove(struct device *dev,
>>> @@ -230,7 +239,11 @@ static int stm32_timers_probe(struct platform_device *pdev)
>>>
>>> stm32_timers_get_arr_size(ddata);
>>>
>>> - stm32_timers_dma_probe(dev, ddata);
>>> + ret = stm32_timers_dma_probe(dev, ddata);
>>> + if (ret) {
>>> + stm32_timers_dma_remove(dev, ddata);
>>
>> With that, stm32_timers_dma_remove() likely need to be updated:
>>
>> - if (ddata->dma.chans[i])
>> + if (!IS_ERR_OR_NULL(ddata->dma.chans[i]))
>> dma_release_channel(ddata->dma.chans[i]);
>>
>> Best regards,
>> Fabrice
>>
>>> + return ret;
>>> + }
>>>
>>> platform_set_drvdata(pdev, ddata);
>>>
>>>
>
> Kind regards,
> - Péter
>
> Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
> Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki
>

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