linux-kernel - Re: [PATCH] gpu: drm: Use devm_clk_get

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Message-ID: <CAGRGNgXn94ZPROLN4JButpnc+ffFFr1SwtTFM=bvcPH95DFQgQ@mail.gmail.com>
Date: Thu, 22 Aug 2024 10:35:45 +1000
From: Julian Calaby <julian.calaby@...il.com>
To: Rong Qianfeng <rongqianfeng@...o.com>
Cc: Stefan Agner <stefan@...er.ch>, Alison Wang <alison.wang@....com>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>, 
	Chen-Yu Tsai <wens@...e.org>, Jernej Skrabec <jernej.skrabec@...il.com>, 
	Samuel Holland <samuel@...lland.org>, dri-devel@...ts.freedesktop.org, 
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-sunxi@...ts.linux.dev, opensource.kernel@...o.com
Subject: Re: [PATCH] gpu: drm: Use devm_clk_get_enabled() helpers

Hi Rong,

On Tue, Aug 20, 2024 at 10:59 PM Rong Qianfeng <rongqianfeng@...o.com> wrote:
>
> Replace devm_clk_get() and clk_prepare_enable() with
> devm_clk_get_enabled() that also disables and unprepares it on
> driver detach.
>
> Signed-off-by: Rong Qianfeng <rongqianfeng@...o.com>
> ---
>  drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c | 13 +++----------
>  drivers/gpu/drm/sun4i/sun6i_drc.c         | 15 ++++-----------
>  drivers/gpu/drm/sun4i/sun8i_mixer.c       | 13 +++----------
>  3 files changed, 10 insertions(+), 31 deletions(-)
>
> diff --git a/drivers/gpu/drm/sun4i/sun6i_drc.c b/drivers/gpu/drm/sun4i/sun6i_drc.c
> index 0d342f43fa93..f263ad282828 100644
> --- a/drivers/gpu/drm/sun4i/sun6i_drc.c
> +++ b/drivers/gpu/drm/sun4i/sun6i_drc.c
> @@ -42,33 +42,28 @@ static int sun6i_drc_bind(struct device *dev, struct device *master,
>                 return ret;
>         }
>
> -       drc->bus_clk = devm_clk_get(dev, "ahb");
> +       drc->bus_clk = devm_clk_get_enabled(dev, "ahb");
>         if (IS_ERR(drc->bus_clk)) {
>                 dev_err(dev, "Couldn't get our bus clock\n");
>                 ret = PTR_ERR(drc->bus_clk);
>                 goto err_assert_reset;
>         }
> -       clk_prepare_enable(drc->bus_clk);
>
> -       drc->mod_clk = devm_clk_get(dev, "mod");
> +       drc->mod_clk = devm_clk_get_enabled(dev, "mod");
>         if (IS_ERR(drc->mod_clk)) {
>                 dev_err(dev, "Couldn't get our mod clock\n");
>                 ret = PTR_ERR(drc->mod_clk);
> -               goto err_disable_bus_clk;
> +               goto err_assert_reset;
>         }
>
>         ret = clk_set_rate_exclusive(drc->mod_clk, 300000000);
>         if (ret) {
>                 dev_err(dev, "Couldn't set the module clock frequency\n");
> -               goto err_disable_bus_clk;
> +               goto err_assert_reset;
>         }
>
> -       clk_prepare_enable(drc->mod_clk);

Am I reading this right: is this changing the init sequence so that
the clock is enabled before setting a rate?

This is the sort of thing that might cause glitches and issues in some
hardware, so it'd be polite to test such a change on the actual
hardware before posting it.

Thanks,

-- 
Julian Calaby

Email: julian.calaby@...il.com
Profile: http://www.google.com/profiles/julian.calaby/