device/azalia_device.c: Always read-write GCAP

In the HD Audio Specification Rev. 1.0a, every bitfield in the GCAP
register is RO (Read Only). However, it is known that in some Intel
PCHs (e.g 6-series and 7-series, documents 324645 and 326776), some
of the bitfields in the GCAP register are R/WO (Read / Write Once).
GCAP is RO on 5-series PCHs; 8-series and 9-series PCHs have a lock
bit for GCAP elsewhere.

Lock GCAP by reading GCAP and writing back the same value. This has
no effect on platforms that implement GCAP as a RO register or lock
GCAP through a different mechanism.

Change-Id: Id61e6976a455273e8c681dbeb4bad35d57b1a8a2
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/83218
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>

src/device/Kconfig

@@ -575,15 +575,6 @@ config AZALIA_HDA_CODEC_SUPPORT
 	  mainboard directory to the build which contain the board-specific HD
 	  audio codec configuration.
 
-config AZALIA_LOCK_DOWN_R_WO_GCAP
-	def_bool n
-	depends on AZALIA_HDA_CODEC_SUPPORT
-	help
-	  The GCAP register is implemented as R/WO (Read / Write Once) on some
-	  HD Audio controllers, such as Intel 6-series PCHs. Select this option
-	  to lock down the GCAP register after deasserting the controller reset
-	  bit. Locking is done by reading GCAP and writing back the read value.
-
 config PCIEXP_PLUGIN_SUPPORT
 	bool
 	default y

src/device/azalia_device.c

@@ -56,10 +56,19 @@ static u16 codec_detect(u8 *base)
 	if (azalia_exit_reset(base) < 0)
 		goto no_codec;
 
-	if (CONFIG(AZALIA_LOCK_DOWN_R_WO_GCAP)) {
-		/* If GCAP is R/WO, lock it down after deasserting controller reset */
-		write16(base + HDA_GCAP_REG, read16(base + HDA_GCAP_REG));
-	}
+	/*
+	 * In the HD Audio Specification Rev. 1.0a, every bitfield in the GCAP
+	 * register is RO (Read Only). However, it is known that in some Intel
+	 * PCHs (e.g 6-series and 7-series, documents 324645 and 326776), some
+	 * of the bitfields in the GCAP register are R/WO (Read / Write Once).
+	 * GCAP is RO on 5-series PCHs; 8-series and 9-series PCHs have a lock
+	 * bit for GCAP elsewhere.
+	 *
+	 * Lock GCAP by reading GCAP and writing back the same value. This has
+	 * no effect on platforms that implement GCAP as a RO register or lock
+	 * GCAP through a different mechanism.
+	 */
+	write16(base + HDA_GCAP_REG, read16(base + HDA_GCAP_REG));
 
 	/* clear STATESTS bits (BAR + 0x0e)[14:0] */
 	reg16 = read16(base + HDA_STATESTS_REG);

src/soc/intel/common/block/hda/Kconfig

@@ -8,6 +8,5 @@ config SOC_INTEL_COMMON_BLOCK_HDA
 config SOC_INTEL_COMMON_BLOCK_HDA_VERB
 	bool
 	depends on SOC_INTEL_COMMON_BLOCK_HDA
-	select AZALIA_LOCK_DOWN_R_WO_GCAP
 	help
 	  Enable initialization of HDA codecs.