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

Fabrice Gasnier
2018-01-23T15:52:49Z

On 01/23/2018 04:30 PM, Lee Jones wrote:
> 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@st.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.

Hi Lee,

Ok, I'll add a comment in v2.

>
>>>> + }
>>>> + 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?

Ok, got it now. I'll do this in v2.

>
>>>> +}
>>>> +
>>>> 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?
>

I guess you've had a look at [PATCH 5/8] pwm: stm32: add capture
support. Are you talking about passing phys_base + TIM_DMAR ?

If this is the case, I'd prefer to keep phys base only if you don't
mind, and handle TIM_DMAR offset in pwm driver. This way, all dma slave
config is kept locally at one place.
Or do you mean something else ?

Maybe I can add a comment here about this ?
Something like:
/* phys_base to be used by child driver, e.g. DMA burst mode */

Please advise,
Thanks,
Fabrice