Re: [PATCH v2] mfd: stm32-timers: Use dma_request_chan() instead dma_request_slave_channel()

[Peter Ujfalusi]

On 16/04/2020 11.46, Lee Jones wrote:
> On Tue, 07 Jan 2020, 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@xxxxxx>
>> ---
>> Hi,
>>
>> Changes since v1:
>> - Fall back to PIO mode only in case of ENODEV and report all other errors
>>
>> Regards,
>> Peter
>>
>>  drivers/mfd/stm32-timers.c | 32 +++++++++++++++++++++++---------
>>  1 file changed, 23 insertions(+), 9 deletions(-)
> 
> Apologies for not spotting this patch sooner, it had slipped through
> the net.  If this happens again, please just submit a [RESEND].

No issues, I have also forgot about it ;)


>> diff --git a/drivers/mfd/stm32-timers.c b/drivers/mfd/stm32-timers.c
>> index efcd4b980c94..add603359124 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 +180,23 @@ 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])) {
>> +			/* Save the first error code to return */
>> +			if (PTR_ERR(ddata->dma.chans[i]) != -ENODEV && !ret)
>> +				ret = PTR_ERR(ddata->dma.chans[i]);
>> +
>> +			ddata->dma.chans[i] = NULL;
>> +		}
>> +	}
> 
> In my mind, it doesn't make sense to keep requesting channels if an
> error has occurred.  Please remove all of the added complexity caused
> by the for() loop and simply check the return value after each call to
> dma_request_chan(), returning immediately on error.

Yes. I have intentionally done the patch this way to _not_ change the
behavior in any ways as it is not up to me to decide what is good or bad
for a driver I can not test.

> 
>> +	return ret;
>>  }
> 

- PÃter

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