Re: [RESEND PATCH v2 4/8] mfd: stm32-timers: add support for dmas

Lee Jones
2018-03-29T12:59:12Z

On Wed, 28 Mar 2018, Fabrice Gasnier wrote:

> On 03/28/2018 05:22 PM, Lee Jones wrote:
> > On Wed, 14 Feb 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 add routine to implement burst reads using DMA from timer registers.
> >> This is exported. So, it can be used by child drivers, PWM capture
> >> for instance (but not limited to).
> >>
> >> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
> >> Reviewed-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
> >> ---
> >> Changes in v2:
> >> - Abstract DMA handling from child driver: move it to MFD core
> >> - Add comments on optional dma support
> >> ---
> >> drivers/mfd/stm32-timers.c | 215 ++++++++++++++++++++++++++++++++++++++-
> >> include/linux/mfd/stm32-timers.h | 27 +++++
> >> 2 files changed, 238 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/drivers/mfd/stm32-timers.c b/drivers/mfd/stm32-timers.c
> >> index a6675a4..2cdad2c 100644
> >> --- a/drivers/mfd/stm32-timers.c
> >> +++ b/drivers/mfd/stm32-timers.c

[...]

> >> + struct dma_chan *dmas[STM32_TIMERS_MAX_DMAS];
> >> + struct stm32_timers ddata;
> >
> > This looks odd to me. Why can't you expand the current ddata
> > structure? Wouldn't it be better to create a stm32_timers_dma
> > structure to place all this information in (except *dev, that should
> > live in the ddata struct), then place a reference in the existing
> > stm32_timers struct?
>
> Maybe I miss-understand you here, from what we discussed in V1:
> https://lkml.org/lkml/2018/1/23/574
> >... "passing in the physical address of the parent MFD into
> > a child device doesn't quite sit right with me"
> I introduced this private struct in MFD parent, and completely hide it
> from the child.
>
> So, do you suggest to add struct definition here ? But make it part of
> struct stm32_timers *ddata?
>
> And only put declaration in include/linux/mfd/stm32-timers.h:
> + struct stm32_timers_dma;
>
> struct stm32_timers {
> struct clk *clk;
> struct regmap *regmap;
> u32 max_arr;
> + struct stm32_timers_dma;
> };

Yes, that's the basic idea.

> I can probably spare the *dev then... use dev->parent in child driver.

What would you use dev->parent for?

[...]

> >> +static int stm32_timers_remove(struct platform_device *pdev)
> >> +{
> >> + struct stm32_timers *ddata = platform_get_drvdata(pdev);
> >> + struct stm32_timers_priv *priv = to_stm32_timers_priv(ddata);
> >> +
> >> + of_platform_depopulate(&pdev->dev);
> >
> > Why can't you continue using devm_*?
>
> I can use devm_of_platform_depopulate() here if you prefer, and keep
> devm_of_platform_populate() in probe.

The point of devm_* is that you don't have to call depopulate.

It happens automatically once this driver is unbound.

--
Lee Jones [李琼斯]
Linaro Services Technical Lead
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