Re: drm/etnaviv: disable MLCG and pulse eater on GPU reset

[Sui Jingfeng <suijingfeng@loongson.cn>]

Hi, Lucas


I love your patch, perhaps something to improve:

The MLCG stand for "Module Level Clock Gating",

without reading the commit message, I guess there may have people don't 
know its meaning.

There are still more thing in this patch can only be understand relay on 
guessing... :-)


But drm/etnaviv drvier still works with this patch applied, so


On 2023/6/7 20:58, Lucas Stach wrote:
> Module level clock gating and the pulse eater might interfere with
> the GPU reset, as they both have the potential to stop the clock
> and thus reset propagation to parts of the GPU.
>
> Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
> Reviewed-by: Christian Gmeiner <cgmeiner@igalia.com>


Tested-by: Sui Jingfeng <suijingfeng@loongson.cn>


> ---
> I'm not aware of any cases where this would have been an issue, but
> it is what the downstream driver does and fundametally seems like
> the right thing to do.
> ---
>   drivers/gpu/drm/etnaviv/etnaviv_gpu.c | 13 ++++++++++++-
>   1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gpu.c b/drivers/gpu/drm/etnaviv/etnaviv_gpu.c
> index de8c9894967c..41aab1aa330b 100644
> --- a/drivers/gpu/drm/etnaviv/etnaviv_gpu.c
> +++ b/drivers/gpu/drm/etnaviv/etnaviv_gpu.c
> @@ -505,8 +505,19 @@ static int etnaviv_hw_reset(struct etnaviv_gpu *gpu)
>   	timeout = jiffies + msecs_to_jiffies(1000);
>   
>   	while (time_is_after_jiffies(timeout)) {
> -		/* enable clock */
>   		unsigned int fscale = 1 << (6 - gpu->freq_scale);
> +		u32 pulse_eater = 0x01590880;
> +
> +		/* disable clock gating */
> +		gpu_write_power(gpu, VIVS_PM_POWER_CONTROLS, 0x0);
> +
> +		/* disable pulse eater */
> +		pulse_eater |= BIT(17);
> +		gpu_write_power(gpu, VIVS_PM_PULSE_EATER, pulse_eater);
> +		pulse_eater |= BIT(0);
> +		gpu_write_power(gpu, VIVS_PM_PULSE_EATER, pulse_eater);
> +
> +		/* enable clock */
>   		control = VIVS_HI_CLOCK_CONTROL_FSCALE_VAL(fscale);
>   		etnaviv_gpu_load_clock(gpu, control);
>   

-- 
Jingfeng