[PATCH 4/9] drm/panfrost: Handle HW_ISSUE_TTRX_3076

[Steven Price]

On 11/02/2022 20:27, alyssa.rosenzweig at collabora.com wrote:
> From: Alyssa Rosenzweig <alyssa.rosenzweig at collabora.com>
> 
> Some Valhall GPUs require resets when encountering bus faults due to
> occlusion query writes. Add the issue bit for this and handle it.
> 
> Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig at collabora.com>

Reviewed-by: Steven Price <steven.price at arm.com>
(although one nit below)

Just in case any one is wondering - these bus faults occur when
switching the GPU's MMU to unmapped - it's not a normal "bus fault" from
the external bus. This is triggered by an attempt to read unmapped
memory which is completed by the driver by switching the entire MMU to
unmapped.

> ---
>  drivers/gpu/drm/panfrost/panfrost_device.c | 9 +++++++--
>  drivers/gpu/drm/panfrost/panfrost_issues.h | 4 ++++
>  2 files changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_device.c b/drivers/gpu/drm/panfrost/panfrost_device.c
> index 7f51a4682ccb..ee612303f076 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_device.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_device.c
> @@ -11,6 +11,7 @@
>  #include "panfrost_device.h"
>  #include "panfrost_devfreq.h"
>  #include "panfrost_features.h"
> +#include "panfrost_issues.h"
>  #include "panfrost_gpu.h"
>  #include "panfrost_job.h"
>  #include "panfrost_mmu.h"
> @@ -380,9 +381,13 @@ const char *panfrost_exception_name(u32 exception_code)
>  bool panfrost_exception_needs_reset(const struct panfrost_device *pfdev,
>  				    u32 exception_code)
>  {
> -	/* Right now, none of the GPU we support need a reset, but this
> -	 * might change.
> +	/* If an occlusion query write causes a bus fault on affected GPUs,
> +	 * future fragment jobs may hang. Reset to workaround.
>  	 */
> +	if (exception_code == DRM_PANFROST_EXCEPTION_JOB_BUS_FAULT)
> +		return panfrost_has_hw_issue(pfdev, HW_ISSUE_TTRX_3076);
> +
> +	/* No other GPUs we support need a reset */
>  	return false;
>  }
>  
> diff --git a/drivers/gpu/drm/panfrost/panfrost_issues.h b/drivers/gpu/drm/panfrost/panfrost_issues.h
> index a66692663833..058f6a4c8435 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_issues.h
> +++ b/drivers/gpu/drm/panfrost/panfrost_issues.h
> @@ -128,6 +128,10 @@ enum panfrost_hw_issue {
>  	/* Must set SC_VAR_ALGORITHM */
>  	HW_ISSUE_TTRX_2968_TTRX_3162,
>  
> +	/* Bus fault from occlusion query write may cause future fragment jobs
> +	 * to hang */

NIT: Kernel comment style has the "/*" and "*/" on lines by themselves
for multi-line comments. checkpatch will complain!

> +	HW_ISSUE_TTRX_3076,
> +
>  	HW_ISSUE_END
>  };
>