Re: [PATCH] drm/xe/xe_guc_ads: Add whitelist registers to write list

[John Harrison <john.c.harrison@intel.com>]

On 11/1/2024 11:04, Jonathan Cavitt wrote:
> When performing a guc_mmio_regset_write, we add all the registers in the
> reg_sr list to the save/restore list, but do not do the same for the
> whitelist registers.  Add them in.
>
> Closes: https://gitlab.freedesktop.org/drm/xe/kernel/issues/2249
> Signed-off-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
> CC: Lucas de Marchi <lucas.demarchi@intel.com>
> CC: Matt Roper <matthew.d.roper@intel.com>
> CC: John Harrison <john.c.harrison@intel.com>
> CC: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
> CC: Ashutosh Dixit <ashutosh.dixit@intel.com>
> ---
>   drivers/gpu/drm/xe/xe_guc_ads.c | 11 ++++++++++-
>   1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/xe/xe_guc_ads.c b/drivers/gpu/drm/xe/xe_guc_ads.c
> index 943146e5b460..2fc6b1ccc8fc 100644
> --- a/drivers/gpu/drm/xe/xe_guc_ads.c
> +++ b/drivers/gpu/drm/xe/xe_guc_ads.c
> @@ -239,9 +239,12 @@ static size_t calculate_regset_size(struct xe_gt *gt)
>   	enum xe_hw_engine_id id;
>   	unsigned int count = 0;
>   
> -	for_each_hw_engine(hwe, gt, id)
> +	for_each_hw_engine(hwe, gt, id) {
>   		xa_for_each(&hwe->reg_sr.xa, sr_idx, sr_entry)
>   			count++;
> +		xa_for_each(&hwe->reg_whitelist.xa, sr_idx, sr_entry)
> +			count++;
> +	}
>   
>   	count += ADS_REGSET_EXTRA_MAX * XE_NUM_HW_ENGINES;
>   
> @@ -727,6 +730,12 @@ static unsigned int guc_mmio_regset_write(struct xe_guc_ads *ads,
>   	xa_for_each(&hwe->reg_sr.xa, idx, entry)
>   		guc_mmio_regset_write_one(ads, regset_map, entry->reg, count++);
>   
> +	i = 0;
> +	xa_for_each(&hwe->reg_whitelist.xa, idx, entry)
> +		guc_mmio_regset_write_one(ads, regset_map,
> +					  RING_FORCE_TO_NONPRIV(hwe->mmio_base, i++),
> +					  count++);
> +
The code that actually writes to the NONPRIV registers 
(xe_reg_sr_apply_whitelist() in xe_reg_src.c) explicitly clears all the 
unused registers with a comment of "clear the rest in case of garbage". 
If we don't trust the reset state to be valid then we need to ensure all 
of them are saved/restored across a reset. Otherwise, that garbage can 
come back and cause problems.

John.


>   	for (e = extra_regs; e < extra_regs + ARRAY_SIZE(extra_regs); e++) {
>   		if (e->skip)
>   			continue;