Re: [v3 PATCH 2/2] drm/i915/guc: Update sizes of CTB buffers

From: Daniel Vetter <daniel@ffwll.ch>
To: Matthew Brost <matthew.brost@intel.com>
Cc: daniel.vetter@intel.com, intel-gfx@lists.freedesktop.org,
	dri-devel@lists.freedesktop.org
Subject: Re: [v3 PATCH 2/2] drm/i915/guc: Update sizes of CTB buffers
Date: Fri, 4 Jun 2021 10:20:05 +0200	[thread overview]
Message-ID: <YLniNZjpBz6E24cK@phenom.ffwll.local> (raw)
In-Reply-To: <20210603230408.54856-2-matthew.brost@intel.com>

On Thu, Jun 03, 2021 at 04:04:08PM -0700, Matthew Brost wrote:
> From: Michal Wajdeczko <michal.wajdeczko@intel.com>
> 
> Future GuC will require CTB buffers sizes to be multiple of 4K.
> Make these changes now as this shouldn't impact us too much.
> 
> Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> Reviewed-by: Matthew Brost <matthew.brost@intel.com>
> Cc: John Harrison <john.c.harrison@intel.com>

Assuming this was just rebased?

> ---
>  drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c | 60 ++++++++++++-----------
>  1 file changed, 32 insertions(+), 28 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 ec795d7c3a7d..8d1173032431 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_ct.c
> @@ -38,6 +38,32 @@ static inline struct drm_device *ct_to_drm(struct intel_guc_ct *ct)
>  #define CT_PROBE_ERROR(_ct, _fmt, ...) \
>  	i915_probe_error(ct_to_i915(ct), "CT: " _fmt, ##__VA_ARGS__)
>  
> +/**
> + * DOC: CTB Blob

These are supposed to be pulled into the kerneldoc builds, but that's not
happening in this patch?

Now I think the GuC docs in general are fairly outdated, so is the DOC
review coming later, or is the DOC: header here simply cargo-culted :-)

If it's not coming later we need to do a JIRA to clean this all up and
link all the new/changed kerneldoc into our GuC doc structure.
-Daniel

> + *
> + * We allocate single blob to hold both CTB descriptors and buffers:
> + *
> + *      +--------+-----------------------------------------------+------+
> + *      | offset | contents                                      | size |
> + *      +========+===============================================+======+
> + *      | 0x0000 | H2G `CTB Descriptor`_ (send)                  |      |
> + *      +--------+-----------------------------------------------+  4K  |
> + *      | 0x0800 | G2H `CTB Descriptor`_ (recv)                  |      |
> + *      +--------+-----------------------------------------------+------+
> + *      | 0x1000 | H2G `CT Buffer`_ (send)                       | n*4K |
> + *      |        |                                               |      |
> + *      +--------+-----------------------------------------------+------+
> + *      | 0x1000 | G2H `CT Buffer`_ (recv)                       | m*4K |
> + *      | + n*4K |                                               |      |
> + *      +--------+-----------------------------------------------+------+
> + *
> + * Size of each `CT Buffer`_ must be multiple of 4K.
> + * As we don't expect too many messages, for now use minimum sizes.
> + */
> +#define CTB_DESC_SIZE		ALIGN(sizeof(struct guc_ct_buffer_desc), SZ_2K)
> +#define CTB_H2G_BUFFER_SIZE	(SZ_4K)
> +#define CTB_G2H_BUFFER_SIZE	(SZ_4K)
> +
>  struct ct_request {
>  	struct list_head link;
>  	u32 fence;
> @@ -175,29 +201,7 @@ int intel_guc_ct_init(struct intel_guc_ct *ct)
>  
>  	GEM_BUG_ON(ct->vma);
>  
> -	/* We allocate 1 page to hold both descriptors and both buffers.
> -	 *       ___________.....................
> -	 *      |desc (SEND)|                   :
> -	 *      |___________|                   PAGE/4
> -	 *      :___________....................:
> -	 *      |desc (RECV)|                   :
> -	 *      |___________|                   PAGE/4
> -	 *      :_______________________________:
> -	 *      |cmds (SEND)                    |
> -	 *      |                               PAGE/4
> -	 *      |_______________________________|
> -	 *      |cmds (RECV)                    |
> -	 *      |                               PAGE/4
> -	 *      |_______________________________|
> -	 *
> -	 * Each message can use a maximum of 32 dwords and we don't expect to
> -	 * have more than 1 in flight at any time, so we have enough space.
> -	 * Some logic further ahead will rely on the fact that there is only 1
> -	 * page and that it is always mapped, so if the size is changed the
> -	 * other code will need updating as well.
> -	 */
> -
> -	blob_size = PAGE_SIZE;
> +	blob_size = 2 * CTB_DESC_SIZE + CTB_H2G_BUFFER_SIZE + CTB_G2H_BUFFER_SIZE;
>  	err = intel_guc_allocate_and_map_vma(guc, blob_size, &ct->vma, &blob);
>  	if (unlikely(err)) {
>  		CT_PROBE_ERROR(ct, "Failed to allocate %u for CTB data (%pe)\n",
> @@ -209,17 +213,17 @@ int intel_guc_ct_init(struct intel_guc_ct *ct)
>  
>  	/* store pointers to desc and cmds for send ctb */
>  	desc = blob;
> -	cmds = blob + PAGE_SIZE / 2;
> -	cmds_size = PAGE_SIZE / 4;
> +	cmds = blob + 2 * CTB_DESC_SIZE;
> +	cmds_size = CTB_H2G_BUFFER_SIZE;
>  	CT_DEBUG(ct, "%s desc %#tx cmds %#tx size %u\n", "send",
>  		 ptrdiff(desc, blob), ptrdiff(cmds, blob), cmds_size);
>  
>  	guc_ct_buffer_init(&ct->ctbs.send, desc, cmds, cmds_size);
>  
>  	/* store pointers to desc and cmds for recv ctb */
> -	desc = blob + PAGE_SIZE / 4;
> -	cmds = blob + PAGE_SIZE / 4 + PAGE_SIZE / 2;
> -	cmds_size = PAGE_SIZE / 4;
> +	desc = blob + CTB_DESC_SIZE;
> +	cmds = blob + 2 * CTB_DESC_SIZE + CTB_H2G_BUFFER_SIZE;
> +	cmds_size = CTB_G2H_BUFFER_SIZE;
>  	CT_DEBUG(ct, "%s desc %#tx cmds %#tx size %u\n", "recv",
>  		 ptrdiff(desc, blob), ptrdiff(cmds, blob), cmds_size);
>  
> -- 
> 2.28.0
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch