Change in coreboot[master]: sb/amd/pi/hudson/early_init: fix setting SPI_USE_SPI100 in SPI100_ENABLE

[Felix Held (Code Review)]

Felix Held has submitted this change. ( https://review.coreboot.org/c/coreboot/+/59934 )

Change subject: sb/amd/pi/hudson/early_init: fix setting SPI_USE_SPI100 in SPI100_ENABLE
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sb/amd/pi/hudson/early_init: fix setting SPI_USE_SPI100 in SPI100_ENABLE

Use a read modify write sequence when setting the SPI_USE_SPI100 bit in
the SPI100_ENABLE register. This avoids clearing other bits in the
register which might cause instabilities. Haven't checked the reference
code, but the register descriptions suggested that the register in
Mullins behaves similar to the one in Stoneyridge. Right now this code
is unused, but it's probably still a good idea to fix it.

TEST=Booting Debian 11 with kernel 5.10 on apu2 still works when adding
a call to hudson_set_spi100 with this patch applied.

Signed-off-by: Felix Held 
Change-Id: Ifbd960a9509542b28f03326a3066995540260bef
Tested-by: Michał Żygowski 
Reviewed-on: https://review.coreboot.org/c/coreboot/+/59934
Tested-by: build bot (Jenkins) 
Reviewed-by: Marshall Dawson 
Reviewed-by: Michał Żygowski 
---
M src/southbridge/amd/pi/hudson/early_setup.c
1 file changed, 2 insertions(+), 1 deletion(-)

Approvals:
  build bot (Jenkins): Verified
  Marshall Dawson: Looks good to me, approved
  Michał Żygowski: Looks good to me, approved

diff --git a/src/southbridge/amd/pi/hudson/early_setup.c b/src/southbridge/amd/pi/hudson/early_setup.c
index 20597d4..2617985 100644
--- a/src/southbridge/amd/pi/hudson/early_setup.c
+++ b/src/southbridge/amd/pi/hudson/early_setup.c
@@ -215,7 +215,8 @@
    			(fast << SPI_FAST_SPEED_NEW_SH) |
    			(alt << SPI_ALT_SPEED_NEW_SH) |
    			(tpm << SPI_TPM_SPEED_NEW_SH));
-	write16((void *)(base + SPI100_ENABLE), SPI_USE_SPI100);
+	write16((void *)(base + SPI100_ENABLE), SPI_USE_SPI100 |
+		read16((void *)(base + SPI100_ENABLE)));
 }

void hudson_disable_4dw_burst(void)

2 is the latest approved patch-set.
No files were changed between the latest approved patch-set and the submitted one.