On Tue, Jul 18, 2023 at 08:18:32PM +0200, 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 devm_pwmchip_alloc().
...
> +void *pwmchip_priv(struct pwm_chip *chip)
> +{
> + return (char *)chip + ALIGN(sizeof(*chip), 32);
Why 32? I haven't found any explanation on the choice. I can understand arch
minimum align, but hard coded value is a bit hard to get.
> +}
...
> +struct pwm_chip *devm_pwmchip_alloc(struct device *parent, size_t sizeof_priv)
> +{
> + struct pwm_chip *chip;
> + size_t alloc_size;
> + alloc_size = ALIGN(sizeof(*chip), 32) + sizeof_priv;
Ditto.
Shouldn't it use a macro from overflow.h?
> + chip = devm_kzalloc(parent, alloc_size, GFP_KERNEL);
> + if (!chip)
> + return NULL;
> +
> + chip->dev = parent;
> +
> + return chip;
> +}
--
With Best Regards,
Andy Shevchenko
