Re: [RFC PATCH 3/4] drm/etnaviv: Change order of enabling clocks to fix boot on i.MX8MM

[Lucas Stach <l.stach@pengutronix.de>]

Am Donnerstag, den 30.04.2020, 12:46 +0000 schrieb Schrempf Frieder:
> From: Frieder Schrempf <frieder.schrempf@kontron.de>
> 
> On some i.MX8MM devices the boot hangs when enabling the GPU clocks.
> Changing the order of clock initalization to
> 
> core -> shader -> bus -> reg
> 
> fixes the issue. This is the same order used in the imx platform code
> of the downstream GPU driver in the NXP kernel [1]. For the sake of
> consistency we also adjust the order of disabling the clocks to the
> reverse.
> 
> [1] https://source.codeaurora.org/external/imx/linux-imx/tree/drivers/mxc/gpu-viv/hal/os/linux/kernel/platform/freescale/gc_hal_kernel_platform_imx.c?h=imx_5.4.3_2.0.0#n1538

I don't see why the order of the clocks is important. Is this really a
GPU issue? As in: does a GPU access hang when enabling the clocks in
the wrong order? Or is this a clock driver issue with a clock access
hanging due to an upstream clock still being disabled?

Regards,
Lucas

> Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>
> ---
>  drivers/gpu/drm/etnaviv/etnaviv_gpu.c | 42 +++++++++++++--------------
>  1 file changed, 21 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gpu.c b/drivers/gpu/drm/etnaviv/etnaviv_gpu.c
> index 7b138d4dd068..424b2e5951f0 100644
> --- a/drivers/gpu/drm/etnaviv/etnaviv_gpu.c
> +++ b/drivers/gpu/drm/etnaviv/etnaviv_gpu.c
> @@ -1487,55 +1487,55 @@ static int etnaviv_gpu_clk_enable(struct etnaviv_gpu *gpu)
>  {
>  	int ret;
>  
> -	if (gpu->clk_reg) {
> -		ret = clk_prepare_enable(gpu->clk_reg);
> +	if (gpu->clk_core) {
> +		ret = clk_prepare_enable(gpu->clk_core);
>  		if (ret)
>  			return ret;
>  	}
>  
> -	if (gpu->clk_bus) {
> -		ret = clk_prepare_enable(gpu->clk_bus);
> +	if (gpu->clk_shader) {
> +		ret = clk_prepare_enable(gpu->clk_shader);
>  		if (ret)
> -			goto disable_clk_reg;
> +			goto disable_clk_core;
>  	}
>  
> -	if (gpu->clk_core) {
> -		ret = clk_prepare_enable(gpu->clk_core);
> +	if (gpu->clk_bus) {
> +		ret = clk_prepare_enable(gpu->clk_bus);
>  		if (ret)
> -			goto disable_clk_bus;
> +			goto disable_clk_shader;
>  	}
>  
> -	if (gpu->clk_shader) {
> -		ret = clk_prepare_enable(gpu->clk_shader);
> +	if (gpu->clk_reg) {
> +		ret = clk_prepare_enable(gpu->clk_reg);
>  		if (ret)
> -			goto disable_clk_core;
> +			goto disable_clk_bus;
>  	}
>  
>  	return 0;
>  
> -disable_clk_core:
> -	if (gpu->clk_core)
> -		clk_disable_unprepare(gpu->clk_core);
>  disable_clk_bus:
>  	if (gpu->clk_bus)
>  		clk_disable_unprepare(gpu->clk_bus);
> -disable_clk_reg:
> -	if (gpu->clk_reg)
> -		clk_disable_unprepare(gpu->clk_reg);
> +disable_clk_shader:
> +	if (gpu->clk_shader)
> +		clk_disable_unprepare(gpu->clk_shader);
> +disable_clk_core:
> +	if (gpu->clk_core)
> +		clk_disable_unprepare(gpu->clk_core);
>  
>  	return ret;
>  }
>  
>  static int etnaviv_gpu_clk_disable(struct etnaviv_gpu *gpu)
>  {
> +	if (gpu->clk_reg)
> +		clk_disable_unprepare(gpu->clk_reg);
> +	if (gpu->clk_bus)
> +		clk_disable_unprepare(gpu->clk_bus);
>  	if (gpu->clk_shader)
>  		clk_disable_unprepare(gpu->clk_shader);
>  	if (gpu->clk_core)
>  		clk_disable_unprepare(gpu->clk_core);
> -	if (gpu->clk_bus)
> -		clk_disable_unprepare(gpu->clk_bus);
> -	if (gpu->clk_reg)
> -		clk_disable_unprepare(gpu->clk_reg);
>  
>  	return 0;
>  }