Re: [Intel-gfx] [PATCH 1/4] drm/i915/guc: Verify result from CTB (de)register action

[Daniel Vetter <daniel@ffwll.ch>]

On Thu, Jul 01, 2021 at 05:55:10PM +0200, Michal Wajdeczko wrote:
> In commit b839a869dfc9 ("drm/i915/guc: Add support for data
> reporting in GuC responses") we missed the hypothetical case
> that GuC might return positive non-zero value as success data.
> 
> While that would be lucky treated as error case, and at the
> end will result in reporting valid -EIO, in the meantime this
> value will be passed to ERR_PTR that could be misleading.
> 
> v2: rebased
> 
> Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
> Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
> Cc: Dan Carpenter <dan.carpenter@oracle.com>

Return value where all integers are possible is always a bit fragile,
especially here where the meaning additionally depends upon whether you
supply a reply buffer or not.

Would be good to document this with some kerneldoc, but maybe the CTB
interface is a bit too unclear here and that's not worth it (there's at
least a ton of functions/variants that just arent used).

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

> ---
>  drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
> index 43409044528e..a26bb55c0898 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
> @@ -148,12 +148,15 @@ static int guc_action_register_ct_buffer(struct intel_guc *guc, u32 type,
>  		FIELD_PREP(HOST2GUC_REGISTER_CTB_REQUEST_MSG_2_DESC_ADDR, desc_addr),
>  		FIELD_PREP(HOST2GUC_REGISTER_CTB_REQUEST_MSG_3_BUFF_ADDR, buff_addr),
>  	};
> +	int ret;
>  
>  	GEM_BUG_ON(type != GUC_CTB_TYPE_HOST2GUC && type != GUC_CTB_TYPE_GUC2HOST);
>  	GEM_BUG_ON(size % SZ_4K);
>  
>  	/* CT registration must go over MMIO */
> -	return intel_guc_send_mmio(guc, request, ARRAY_SIZE(request), NULL, 0);
> +	ret = intel_guc_send_mmio(guc, request, ARRAY_SIZE(request), NULL, 0);
> +
> +	return ret > 0 ? -EPROTO : ret;
>  }
>  
>  static int ct_register_buffer(struct intel_guc_ct *ct, u32 type,
> @@ -177,11 +180,14 @@ static int guc_action_deregister_ct_buffer(struct intel_guc *guc, u32 type)
>  		FIELD_PREP(GUC_HXG_REQUEST_MSG_0_ACTION, GUC_ACTION_HOST2GUC_DEREGISTER_CTB),
>  		FIELD_PREP(HOST2GUC_DEREGISTER_CTB_REQUEST_MSG_1_TYPE, type),
>  	};
> +	int ret;
>  
>  	GEM_BUG_ON(type != GUC_CTB_TYPE_HOST2GUC && type != GUC_CTB_TYPE_GUC2HOST);
>  
>  	/* CT deregistration must go over MMIO */
> -	return intel_guc_send_mmio(guc, request, ARRAY_SIZE(request), NULL, 0);
> +	ret = intel_guc_send_mmio(guc, request, ARRAY_SIZE(request), NULL, 0);
> +
> +	return ret > 0 ? -EPROTO : ret;
>  }
>  
>  static int ct_deregister_buffer(struct intel_guc_ct *ct, u32 type)
> -- 
> 2.25.1
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch