[PATCH 1/1] drm/bridge: ti-sn65dsi83: Fix enable error path

[Luca Ceresoli]

Hello Alexander,

On Wed, 28 Feb 2024 09:15:46 +0100
Alexander Stein <alexander.stein at ew.tq-group.com> wrote:


[...]

> Oh I mistook this DSI-LVDS bridge with the DSI-DP bridge on a different
> board, my bad. I hope I can provide some insights. My platform is
> imx8mm-tqma8mqml-mba8mx-lvds-tm070jvhg33.dtb.
> I can easily cause a PLL lock failure by reducing the delay for the
> enable-gpios 'gpio_delays'. This will result in a PLL lock faiure.
> On my platform the vcc-supply counters do look sane:
> > /sys/kernel/debug/regulator/SN65DSI83_1V8/open_count:1
> > /sys/kernel/debug/regulator/SN65DSI83_1V8/use_count:0  

Interesting. Thanks for taking time to report your initial issue!

> Once I remove the ti_sn65dsi83 module, the open_count decrements to 0 as
> well. Looks sane to me.
> 
> If I revert commit c81cd8f7c774 ("Revert "drm/bridge: ti-sn65dsi83:
> Fix enable error path""), vcc-supply counters are:
> > /sys/kernel/debug/regulator/SN65DSI83_1V8/open_count:1
> > /sys/kernel/debug/regulator/SN65DSI83_1V8/use_count:1  
> 
> So in my case the use_count does not decrease! If I remove the module
> ti_sn65dsi83, I get the WARN_ON (enable_count is still non-zero):
> > WARNING: CPU: 2 PID: 402 at drivers/regulator/core.c:2398 _regulator_put+0x15c/0x164  
> 
> This is on 6.8.0-rc6-next-20240228 with the following diff applied:
> --->8---  
> diff --git a/arch/arm64/boot/dts/freescale/mba8mx.dtsi b/arch/arm64/boot/dts/freescale/mba8mx.dtsi
> index 427467df42bf..8461e1fd396f 100644
> --- a/arch/arm64/boot/dts/freescale/mba8mx.dtsi
> +++ b/arch/arm64/boot/dts/freescale/mba8mx.dtsi
> @@ -285,7 +285,7 @@ &i2c3 {
>         dsi_lvds_bridge: bridge at 2d {
>                 compatible = "ti,sn65dsi84";
>                 reg = <0x2d>;
> -               enable-gpios = <&gpio_delays 0 130000 0>;
> +               enable-gpios = <&gpio_delays 0 0 0>;
>                 vcc-supply = <&reg_sn65dsi83_1v8>;
>                 status = "disabled";
>  
> diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi83.c b/drivers/gpu/drm/bridge/ti-sn65dsi83.c
> index 4814b7b6d1fd..57a7ed13f996 100644
> --- a/drivers/gpu/drm/bridge/ti-sn65dsi83.c
> +++ b/drivers/gpu/drm/bridge/ti-sn65dsi83.c
> @@ -478,7 +478,6 @@ static void sn65dsi83_atomic_pre_enable(struct drm_bridge *bridge,
>                 dev_err(ctx->dev, "failed to lock PLL, ret=%i\n", ret);
>                 /* On failure, disable PLL again and exit. */
>                 regmap_write(ctx->regmap, REG_RC_PLL_EN, 0x00);
> -               regulator_disable(ctx->vcc);
>                 return;
>         }
> --->8---  
> 
> So my patch indeed did fix an actual problem. On the other hand it seems
> sn65dsi83_atomic_disable is not called in my case for some reason.

So you remove the module and atomic_disable is not called, after
having called atomic_pre_enable?

I'm very possibly missing something, but this looks like a bug in the
DRM bridge code at first sight.

Luca

-- 
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com