drm/xe/guc: Fix h2g_write usage of GUC_CTB_MSG_MAX_LEN

In the ABI header, GUC_CTB_MSG_MIN_LEN is '1' because
GUC_CTB_HDR_LEN is 1. This aligns with H2G/G2H CTB specification
where all command formats are defined in units of dwords so that '1'
is a dword. Accordingly, GUC_CTB_MSG_MAX_LEN is 256-1 (i.e. 255
dwords). However, h2g_write was incorrectly assuming that
GUC_CTB_MSG_MAX_LEN was in bytes. Fix this.

v3: Fix nit on #define location.(Matt)
v2: By correctly treating GUC_CTB_MSG_MAX_LEN as dwords, it causes
    a local array to consume 4x the stack size. Rework the function
    to avoid consuming stack even if the action size is large. (Matt)

Signed-off-by: Alan Previn <alan.previn.teres.alexis@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

diff --git a/drivers/gpu/drm/xe/xe_guc_ct.c b/drivers/gpu/drm/xe/xe_guc_ct.c
index 22bc9ce846db72652a2b6e378fe8cca84182b792..e71d069158dcaa735e888389fa0fb015607ce365 100644 (file)
--- a/drivers/gpu/drm/xe/xe_guc_ct.c
+++ b/drivers/gpu/drm/xe/xe_guc_ct.c
@@ -396,24 +396,27 @@ static void g2h_release_space(struct xe_guc_ct *ct, u32 g2h_len)
        spin_unlock_irq(&ct->fast_lock);
 }
 
+#define H2G_CT_HEADERS (GUC_CTB_HDR_LEN + 1) /* one DW CTB header and one DW HxG header */
+
 static int h2g_write(struct xe_guc_ct *ct, const u32 *action, u32 len,
                     u32 ct_fence_value, bool want_response)
 {
        struct xe_device *xe = ct_to_xe(ct);
        struct guc_ctb *h2g = &ct->ctbs.h2g;
-       u32 cmd[GUC_CTB_MSG_MAX_LEN / sizeof(u32)];
-       u32 cmd_len = len + GUC_CTB_HDR_LEN;
-       u32 cmd_idx = 0, i;
+       u32 cmd[H2G_CT_HEADERS];
        u32 tail = h2g->info.tail;
+       u32 full_len;
        struct iosys_map map = IOSYS_MAP_INIT_OFFSET(&h2g->cmds,
                                                         tail * sizeof(u32));
 
+       full_len = len + GUC_CTB_HDR_LEN;
+
        lockdep_assert_held(&ct->lock);
-       XE_BUG_ON(len * sizeof(u32) > GUC_CTB_MSG_MAX_LEN);
+       XE_BUG_ON(full_len > (GUC_CTB_MSG_MAX_LEN - GUC_CTB_HDR_LEN));
        XE_BUG_ON(tail > h2g->info.size);
 
        /* Command will wrap, zero fill (NOPs), return and check credits again */
-       if (tail + cmd_len > h2g->info.size) {
+       if (tail + full_len > h2g->info.size) {
                xe_map_memset(xe, &map, 0, 0,
                              (h2g->info.size - tail) * sizeof(u32));
                h2g_reserve_space(ct, (h2g->info.size - tail));
@@ -428,30 +431,33 @@ static int h2g_write(struct xe_guc_ct *ct, const u32 *action, u32 len,
         * dw1: HXG header (including action code)
         * dw2+: action data
         */
-       cmd[cmd_idx++] = FIELD_PREP(GUC_CTB_MSG_0_FORMAT, GUC_CTB_FORMAT_HXG) |
+       cmd[0] = FIELD_PREP(GUC_CTB_MSG_0_FORMAT, GUC_CTB_FORMAT_HXG) |
                FIELD_PREP(GUC_CTB_MSG_0_NUM_DWORDS, len) |
                FIELD_PREP(GUC_CTB_MSG_0_FENCE, ct_fence_value);
        if (want_response) {
-               cmd[cmd_idx++] =
+               cmd[1] =
                        FIELD_PREP(GUC_HXG_MSG_0_TYPE, GUC_HXG_TYPE_REQUEST) |
                        FIELD_PREP(GUC_HXG_EVENT_MSG_0_ACTION |
                                   GUC_HXG_EVENT_MSG_0_DATA0, action[0]);
        } else {
-               cmd[cmd_idx++] =
+               cmd[1] =
                        FIELD_PREP(GUC_HXG_MSG_0_TYPE, GUC_HXG_TYPE_EVENT) |
                        FIELD_PREP(GUC_HXG_EVENT_MSG_0_ACTION |
                                   GUC_HXG_EVENT_MSG_0_DATA0, action[0]);
        }
-       for (i = 1; i < len; ++i)
-               cmd[cmd_idx++] = action[i];
+
+       /* H2G header in cmd[1] replaces action[0] so: */
+       --len;
+       ++action;
 
        /* Write H2G ensuring visable before descriptor update */
-       xe_map_memcpy_to(xe, &map, 0, cmd, cmd_len * sizeof(u32));
+       xe_map_memcpy_to(xe, &map, 0, cmd, H2G_CT_HEADERS * sizeof(u32));
+       xe_map_memcpy_to(xe, &map, H2G_CT_HEADERS * sizeof(u32), action, len * sizeof(u32));
        xe_device_wmb(ct_to_xe(ct));
 
        /* Update local copies */
-       h2g->info.tail = (tail + cmd_len) % h2g->info.size;
-       h2g_reserve_space(ct, cmd_len);
+       h2g->info.tail = (tail + full_len) % h2g->info.size;
+       h2g_reserve_space(ct, full_len);
 
        /* Update descriptor */
        desc_write(xe, h2g, tail, h2g->info.tail);