Re: [PATCH 1/2] drm/meson: dw-hdmi: Disable clocks on driver teardown

Marc Zyngier
2020-11-23T14:16:02Z

On 2020-11-23 14:03, Jerome Brunet wrote:
> On Fri 20 Nov 2020 at 10:42, Marc Zyngier <maz@kernel.org> wrote:
>
>> The HDMI driver request clocks early, but never disable them, leaving
>> the clocks on even when the driver is removed.
>>
>> Fix it by slightly refactoring the clock code, and register a devm
>> action that will eventually disable/unprepare the enabled clocks.
>>
>> Signed-off-by: Marc Zyngier <maz@kernel.org>
>> ---
>> drivers/gpu/drm/meson/meson_dw_hdmi.c | 43
>> ++++++++++++++++++---------
>> 1 file changed, 29 insertions(+), 14 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/meson/meson_dw_hdmi.c
>> b/drivers/gpu/drm/meson/meson_dw_hdmi.c
>> index 7f8eea494147..29623b309cb1 100644
>> --- a/drivers/gpu/drm/meson/meson_dw_hdmi.c
>> +++ b/drivers/gpu/drm/meson/meson_dw_hdmi.c
>> @@ -145,8 +145,6 @@ struct meson_dw_hdmi {
>> struct reset_control *hdmitx_apb;
>> struct reset_control *hdmitx_ctrl;
>> struct reset_control *hdmitx_phy;
>> - struct clk *hdmi_pclk;
>> - struct clk *venci_clk;
>> struct regulator *hdmi_supply;
>> u32 irq_stat;
>> struct dw_hdmi *hdmi;
>> @@ -946,6 +944,29 @@ static void meson_disable_regulator(void *data)
>> regulator_disable(data);
>> }
>>
>> +static void meson_disable_clk(void *data)
>> +{
>> + clk_disable_unprepare(data);
>> +}
>> +
>> +static int meson_enable_clk(struct device *dev, char *name)
>> +{
>> + struct clk *clk;
>> + int ret;
>> +
>> + clk = devm_clk_get(dev, name);
>> + if (IS_ERR(clk)) {
>> + dev_err(dev, "Unable to get %s pclk\n", name);
>> + return PTR_ERR(clk);
>> + }
>> +
>> + ret = clk_prepare_enable(clk);
>> + if (!ret)
>> + ret = devm_add_action_or_reset(dev, meson_disable_clk,
>> clk);
>
> Thanks for fixing this Marc.
>
> FYI, while it is fine to declare a function to disable the clocks, a
> quick
> cast may avoid it
>
> devm_add_action_or_reset(dev, (void(*)(void *))clk_disable_unprepare,
> clk);

While this works for now, a change to the clk_disable_unprepare()
prototype (such as adding a second argument) would now go completely
unnoticed (after all, you've cast the function, it *must* be correct,
right?), and someone would spend a few hours trying to track down memory
corruption or some other interesting results.

Yes, casting C functions can be hilarious.

I can see a few uses of this hack in the tree, and I have my pop-corn
ready.

Thanks,

M.
--
Jazz is not dead. It just smells funny...