vgsp: add gsp_phys_rmcall_channel to force one GR channel variant

Lets a bisection pair any promote shape with any channel shape, in
particular V6 (SKIP_CTXBUFFER_ALLOC, KMD-managed) with the server-managed
VA-only promote: with skip-ctxbuffer the server's kgrctxMapCtxBuffers does
not pre-book the engine context vaList, so the VA branch's
vaListSetManaged(NV_FALSE) gate should pass and the per-buffer commit can
program the engine context VA. Default 0 keeps the mode-selected walk
byte-identical. Not hardware-tested (GPU wedged; see Handoff ADDENDUM 51).

1 files changed, 34 insertions, 0 deletions

diff --git a/kernel/gsp_phys_booter.c b/kernel/gsp_phys_booter.c
index fae657c..3a65361 100644
--- a/kernel/gsp_phys_booter.c
+++ b/kernel/gsp_phys_booter.c
@@ -7249,6 +7249,40 @@ static int gsp_phys_rmcall_alloc_channel(void __iomem *bar0)
 		vars = &gsp_phys_rmcall_channel_variants[0];
 		attempts = 1;
 	}
+	/*
+	 * Optional explicit force (gsp_phys_rmcall_channel=N): pin the walk to
+	 * one variant after the mode-based selection so a bisection can pair
+	 * any promote shape with any channel shape (e.g. V6 skip-ctxbuffer +
+	 * the srvctx VA-only promote).
+	 */
+	if (gsp_phys_rmcall_engine_is_gr() &&
+	    gsp_phys_rmcall_channel_value() != 0) {
+		u32 force = (u32)gsp_phys_rmcall_channel_value();
+		u32 j;
+		bool found = false;
+
+		for (j = 0; j < ARRAY_SIZE(gsp_phys_rmcall_channel_variants);
+		     j++) {
+			if (gsp_phys_rmcall_channel_variants[j].id != force)
+				continue;
+			vars = &gsp_phys_rmcall_channel_variants[j];
+			found = true;
+			break;
+		}
+		if (!found &&
+		    gsp_phys_rmcall_channel_variant_skipctx.id == force) {
+			vars = &gsp_phys_rmcall_channel_variant_skipctx;
+			found = true;
+		}
+		if (!found) {
+			pr_err("vgsp-boot: rm-call: gsp_phys_rmcall_channel=%u is not a known variant id (1/3/4/5/6); aborting the ladder\n",
+			       force);
+			return -EINVAL;
+		}
+		attempts = 1;
+		pr_info("vgsp-boot: rm-call: gsp_phys_rmcall_channel=%u forces channel variant V%u (%s) alone\n",
+			force, vars[0].id, vars[0].name);
+	}
 
 	ret = -EIO;
 	for (i = 0; i < attempts; i++) {