[PATCH v6 003/164] pwm: Provide pwmchip_alloc() function and a devm variant of it

[Uwe Kleine-König]

On Wed, Feb 14, 2024 at 02:49:26PM +0200, Andy Shevchenko wrote:
> On Wed, Feb 14, 2024 at 10:30:50AM +0100, Uwe Kleine-König wrote:
> > This function allocates a struct pwm_chip and driver data. Compared to
> > the status quo the split into pwm_chip and driver data is new, otherwise
> > it doesn't change anything relevant (yet).
> > 
> > The intention is that after all drivers are switched to use this
> > allocation function, its possible to add a struct device to struct
> > pwm_chip to properly track the latter's lifetime without touching all
> > drivers again. Proper lifetime tracking is a necessary precondition to
> > introduce character device support for PWMs (that implements atomic
> > setting and doesn't suffer from the sysfs overhead of the /sys/class/pwm
> > userspace support).
> > 
> > The new function pwmchip_priv() (obviously?) only works for chips
> > allocated with pwmchip_alloc().
> 
> ...
> 
> > +#define PWMCHIP_ALIGN ARCH_DMA_MINALIGN
> > +
> > +static void *pwmchip_priv(struct pwm_chip *chip)
> > +{
> > +	return (void *)chip + ALIGN(sizeof(*chip), PWMCHIP_ALIGN);
> > +}
> 
> Why not use dma_get_cache_alignment() ?

Hmm, that function returns 1 if ARCH_HAS_DMA_MINALIGN isn't defined. The
idea of using ARCH_DMA_MINALIGN was to ensure that the priv data has the
same minimal alignment as kmalloc(). Took my inspriration from
https://lore.kernel.org/r/20240209-counter-align-fix-v2-1-5777ea0a2722@analog.com
. The implementation of dma_get_cache_alignment suggests that not all
archs provide ARCH_DMA_MINALIGN? Also there is ARCH_KMALLOC_MINALIGN.
Hmm, don't know yet what to do here.

> > +/* This is the counterpart to pwmchip_alloc */
> 
> pwmchip_alloc()

Ack.
 
> > +EXPORT_SYMBOL_GPL(pwmchip_put);
> 
> > +EXPORT_SYMBOL_GPL(pwmchip_alloc);
> 
> > +EXPORT_SYMBOL_GPL(devm_pwmchip_alloc);
> 
> Are these exported via namespace? If no, can they be from day 1?

I added that to my todo list for all pwm functions. Will address that
separately.

Thanks for your feedback
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |
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