linux-kernel - Re: [PATCH 4/8] mfd: stm32-timers: add support for dmas

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Message-ID: <20180123153035.2rvhspe2m5ej57op@dell>
Date:   Tue, 23 Jan 2018 15:30:35 +0000
From:   Lee Jones <lee.jones@...aro.org>
To:     Fabrice Gasnier <fabrice.gasnier@...com>
Cc:     thierry.reding@...il.com, robh+dt@...nel.org,
        alexandre.torgue@...com, benjamin.gaignard@...aro.org,
        mark.rutland@....com, linux@...linux.org.uk,
        mcoquelin.stm32@...il.com, benjamin.gaignard@...com,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-pwm@...r.kernel.org
Subject: Re: [PATCH 4/8] mfd: stm32-timers: add support for dmas

On Tue, 23 Jan 2018, Fabrice Gasnier wrote:

> On 01/23/2018 02:32 PM, Lee Jones wrote:
> > On Tue, 16 Jan 2018, Fabrice Gasnier wrote:
> > 
> >> STM32 Timers can support up to 7 dma requests:
> >> 4 channels, update, compare and trigger.
> >> Optionally request part, or all dmas from stm32-timers MFD core.
> >> Also, keep reference of device's bus address to allow child drivers to
> >> transfer data from/to device by using dma.
> >>
> >> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@...com>
> >> ---
> >>  drivers/mfd/stm32-timers.c       | 37 ++++++++++++++++++++++++++++++++++++-
> >>  include/linux/mfd/stm32-timers.h | 14 ++++++++++++++
> >>  2 files changed, 50 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/mfd/stm32-timers.c b/drivers/mfd/stm32-timers.c
> >> index a6675a4..372b51e 100644
> >> --- a/drivers/mfd/stm32-timers.c
> >> +++ b/drivers/mfd/stm32-timers.c
> >> @@ -29,6 +29,23 @@ 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,
> >> +				   struct stm32_timers *ddata)
> >> +{
> >> +	int i;
> >> +	char name[4];
> >> +
> >> +	for (i = STM32_TIMERS_DMA_CH1; i <= STM32_TIMERS_DMA_CH4; i++) {
> >> +		snprintf(name, ARRAY_SIZE(name), "ch%1d", i + 1);
> >> +		ddata->dmas[i] = dma_request_slave_channel(dev, name);
> > 
> > And if any of them fail?
> 
> Hi Lee,
> 
> If some of these fails, reference will be NULL. It is checked in child
> driver (pwm for instance) at runtime. Support is being added as an
> option: pwm capture will simply be unavailable in this case (fail with
> error).

Can you place a simple one-line comment in here please.  Or else
someone will come along and add error handling for you.

> >> +	}
> >> +	ddata->dmas[STM32_TIMERS_DMA_UP] = dma_request_slave_channel(dev, "up");
> >> +	ddata->dmas[STM32_TIMERS_DMA_TRIG] =
> >> +		dma_request_slave_channel(dev, "trig");
> >> +	ddata->dmas[STM32_TIMERS_DMA_COM] =
> >> +		dma_request_slave_channel(dev, "com");
> > 
> > Can you format these in the same why.  This hurts my eyes.
> 
> I use enum values and try to match as possible with reference manual for
> "up", "trig" & "com" names.
> Would have some suggestion to beautify this?

I just mean, can you push the first  dma_request_slave_channel() call
on to the next line, so each of the calls are formatted in the same
manner please?

> >> +}
> >> +
> >>  static int stm32_timers_probe(struct platform_device *pdev)
> >>  {
> >>  	struct device *dev = &pdev->dev;
> >> @@ -44,6 +61,7 @@ static int stm32_timers_probe(struct platform_device *pdev)
> >>  	mmio = devm_ioremap_resource(dev, res);
> >>  	if (IS_ERR(mmio))
> >>  		return PTR_ERR(mmio);
> >> +	ddata->phys_base = res->start;
> > 
> > What do you use this for?
> 
> This is used in in child driver (pwm) for capture data transfer by dma.

Might be worth being clear about that.

Perhaps pass in 'dma_base' (phys_base + offset) instead?

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