linux-kernel - Re: [PATCH v2] mfd: stm32-timers: Use dma_request_chan() instead dma_request_slave

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Message-ID: <20200416084651.GW2167633@dell>
Date:   Thu, 16 Apr 2020 09:46:51 +0100
From:   Lee Jones <lee.jones@...aro.org>
To:     Peter Ujfalusi <peter.ujfalusi@...com>
Cc:     fabrice.gasnier@...com, mcoquelin.stm32@...il.com,
        alexandre.torgue@...com, vkoul@...nel.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mfd: stm32-timers: Use dma_request_chan() instead
 dma_request_slave_channel()

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@...com>
> ---
> 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].

> 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.

> +	return ret;
>  }

-- 
Lee Jones [李琼斯]
Linaro Services Technical Lead
Linaro.org │ Open source software for ARM SoCs
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