linux-kernel - Re: [PATCH v5 6/7] pwm: lpss: Add devm_pwm_lpss

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Date:   Tue, 22 Nov 2022 17:47:03 +0100
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Thierry Reding <thierry.reding@...il.com>,
        linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org,
        linux-pwm@...r.kernel.org, Andy Shevchenko <andy@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH v5 6/7] pwm: lpss: Add devm_pwm_lpss_probe() stub

On Thu, Nov 17, 2022 at 01:08:05PM +0200, Andy Shevchenko wrote:
> In case the PWM LPSS module is not provided, allow users to be
> compiled with the help of the devm_pwm_lpss_probe() stub.
> 
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Acked-by: Thierry Reding <thierry.reding@...il.com>
> Reviewed-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
> ---
>  include/linux/platform_data/x86/pwm-lpss.h | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/include/linux/platform_data/x86/pwm-lpss.h b/include/linux/platform_data/x86/pwm-lpss.h
> index c852fe24fe2a..6ef21b8baec7 100644
> --- a/include/linux/platform_data/x86/pwm-lpss.h
> +++ b/include/linux/platform_data/x86/pwm-lpss.h
> @@ -4,6 +4,8 @@
>  #ifndef __PLATFORM_DATA_X86_PWM_LPSS_H
>  #define __PLATFORM_DATA_X86_PWM_LPSS_H
>  
> +#include <linux/err.h>
> +#include <linux/kconfig.h>
>  #include <linux/types.h>
>  
>  struct device;
> @@ -27,7 +29,16 @@ struct pwm_lpss_boardinfo {
>  	bool other_devices_aml_touches_pwm_regs;
>  };
>  
> +#if IS_REACHABLE(CONFIG_PWM_LPSS)
>  struct pwm_lpss_chip *devm_pwm_lpss_probe(struct device *dev, void __iomem *base,
>  					  const struct pwm_lpss_boardinfo *info);
> +#else
> +static inline
> +struct pwm_lpss_chip *devm_pwm_lpss_probe(struct device *dev, void __iomem *base,
> +					  const struct pwm_lpss_boardinfo *info)
> +{
> +	return ERR_PTR(-ENODEV);
> +}
> +#endif	/* CONFIG_PWM_LPSS */

Hmm, this is actually never used, because if
!IS_REACHABLE(CONFIG_PWM_LPSS), the only caller (that is added in patch
7) has:

	if (!IS_REACHABLE(CONFIG_PWM_LPSS))
		return 0;

before devm_pwm_lpss_probe() is called.

Not sure if it's safe to just drop this patch. The return value is
neither -ENOSYS (which I would expect for a stub function like that) nor
-EINVAL (which for reasons unknown to me is used in the stub for
pwmchip_add()).

I would have a better feeling with -ENOSYS in your stub, but I don't
feel really strong here.

Best regards
Uwe

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

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