linux-kernel - Re: [PATCH] mfd: stm32-timers: Use dma_request_chan() instead dma_request_slave

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Date:   Fri, 20 Dec 2019 09:54:01 +0100
From:   Fabrice Gasnier <fabrice.gasnier@...com>
To:     Peter Ujfalusi <peter.ujfalusi@...com>, <lee.jones@...aro.org>,
        <mcoquelin.stm32@...il.com>, <alexandre.torgue@...com>
CC:     <vkoul@...nel.org>, <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        Benjamin GAIGNARD <benjamin.gaignard@...com>
Subject: Re: [PATCH] mfd: stm32-timers: Use dma_request_chan() instead
 dma_request_slave_channel()

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@...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]);

> +
> +			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);
>  
>