[Intel-gfx] [RFC PATCH 14/97] drm/i915/guc: Update sizes of CTB buffers

[Matthew Brost]

On Thu, May 06, 2021 at 12:13:28PM -0700, Matthew Brost wrote:
> From: Michal Wajdeczko <michal.wajdeczko at 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 at intel.com>
> Signed-off-by: Matthew Brost <matthew.brost at intel.com>
> Cc: John Harrison <john.c.harrison at intel.com>
> ---
>  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 c54a29176862..c87a0a8bef26 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
> + *
> + * 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;

2 is a magic number here. Think it would be more clear with
CTB_NUMBER_DESC define here.

Michal what do you think? We can fix this in the next post of this with
your blessing.

With that nit:
Reviewed-by: Matthew Brost <matthew.brost at intel.com> 

> +	cmds_size = CTB_H2G_BUFFER_SIZE;
>  	CT_DEBUG(ct, "%s desc %#lx cmds %#lx 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 %#lx cmds %#lx size %u\n", "recv",
>  		 ptrdiff(desc, blob), ptrdiff(cmds, blob), cmds_size);
>  
> -- 
> 2.28.0
>