drm/xe/pcode: Rework error mapping

The sparse array used for error decoding from is unnecessarily big. It
should be better handled by a switch statement that will also allow us
to more easily improve this code.

Add a CASE_ERR() macro to keep the table compact and use it instead of
the 256-entries array, which saves some space:

$ bloat-o-meter xe_pcode.o.old xe_pcode.o
add/remove: 0/1 grow/shrink: 2/0 up/down: 190/-4096 (-3906)
Function old new delta
__pcode_mailbox_rw 363 465 +102
__pcode_mailbox_rw.cold 58 146 +88
err_decode 4096 - -4096
Total: Before=7890, After=3984, chg -49.51%

Reviewed-by: Raag Jadav <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Lucas De Marchi <[e-mail]>

drivers/gpu/drm/xe/xe_pcode.c

···
 
 static int pcode_mailbox_status(struct xe_tile *tile)
 {
+	const char *err_str;
+	int err_decode;
 	u32 err;
-	static const struct pcode_err_decode err_decode[] = {
-		[PCODE_ILLEGAL_CMD] = {-ENXIO, "Illegal Command"},
-		[PCODE_TIMEOUT] = {-ETIMEDOUT, "Timed out"},
-		[PCODE_ILLEGAL_DATA] = {-EINVAL, "Illegal Data"},
-		[PCODE_ILLEGAL_SUBCOMMAND] = {-ENXIO, "Illegal Subcommand"},
-		[PCODE_LOCKED] = {-EBUSY, "PCODE Locked"},
-		[PCODE_GT_RATIO_OUT_OF_RANGE] = {-EOVERFLOW,
-			"GT ratio out of range"},
-		[PCODE_REJECTED] = {-EACCES, "PCODE Rejected"},
-		[PCODE_ERROR_MASK] = {-EPROTO, "Unknown"},
-	};
+
+#define CASE_ERR(_err, _err_decode, _err_str)	\
+	case _err:				\
+		err_decode = _err_decode;	\
+		err_str = _err_str;		\
+		break
 
 	err = xe_mmio_read32(&tile->mmio, PCODE_MAILBOX) & PCODE_ERROR_MASK;
+	switch (err) {
+	CASE_ERR(PCODE_ILLEGAL_CMD,           -ENXIO,     "Illegal Command");
+	CASE_ERR(PCODE_TIMEOUT,               -ETIMEDOUT, "Timed out");
+	CASE_ERR(PCODE_ILLEGAL_DATA,          -EINVAL,    "Illegal Data");
+	CASE_ERR(PCODE_ILLEGAL_SUBCOMMAND,    -ENXIO,     "Illegal Subcommand");
+	CASE_ERR(PCODE_LOCKED,                -EBUSY,     "PCODE Locked");
+	CASE_ERR(PCODE_GT_RATIO_OUT_OF_RANGE, -EOVERFLOW, "GT ratio out of range");
+	CASE_ERR(PCODE_REJECTED,              -EACCES,    "PCODE Rejected");
+	default:
+		err_decode = -EPROTO;
+		err_str = "Unknown";
+	}
+
 	if (err) {
-		drm_err(&tile_to_xe(tile)->drm, "PCODE Mailbox failed: %d %s", err,
-			err_decode[err].str ?: "Unknown");
-		return err_decode[err].errno ?: -EPROTO;
+		drm_err(&tile_to_xe(tile)->drm, "PCODE Mailbox failed: %d %s",
+			err_decode, err_str);
+
+		return err_decode;
 	}
 
 	return 0;
+#undef CASE_ERR
 }
 
 static int __pcode_mailbox_rw(struct xe_tile *tile, u32 mbox, u32 *data0, u32 *data1,

drivers/gpu/drm/xe/xe_pcode_api.h

···
 #define BMG_PCIE_CAP			XE_REG(0x138340)
 #define   LINK_DOWNGRADE		REG_GENMASK(1, 0)
 #define     DOWNGRADE_CAPABLE		2
-
-struct pcode_err_decode {
-	int errno;
-	const char *str;
-};
-