Change in coreboot[master]: soc/amd/common/block/lpc/spi_dma: Use mutex to protect DMA registers

[Raul Rangel (Code Review)]

Attention is currently required from: Jason Glenesk, Marshall Dawson, Felix Held.
Raul Rangel has uploaded this change for review. ( https://review.coreboot.org/c/coreboot/+/56231 )

Change subject: soc/amd/common/block/lpc/spi_dma: Use mutex to protect DMA registers
......................................................................

soc/amd/common/block/lpc/spi_dma: Use mutex to protect DMA registers

Once we enable COOP_MULTITASKING, we need to guarantee that we don't
have multiple threads trhing to access the DMA hardware.

BUG=b:179699789
TEST=Boot guybrush with APOB patches.

Signed-off-by: Raul E Rangel 
Change-Id: Ibb8e31c95d6722521425772f4210af45626c8e09
---
M src/soc/amd/common/block/lpc/spi_dma.c
1 file changed, 7 insertions(+), 0 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/31/56231/1

diff --git a/src/soc/amd/common/block/lpc/spi_dma.c b/src/soc/amd/common/block/lpc/spi_dma.c
index 9bee259..dede449 100644
--- a/src/soc/amd/common/block/lpc/spi_dma.c
+++ b/src/soc/amd/common/block/lpc/spi_dma.c
@@ -13,6 +13,7 @@
 #include <soc/pci_devs.h>
 #include <spi_flash.h>
 #include <string.h>
+#include <thread.h>
 #include <types.h>

/* The ROM is memory mapped just below 4GiB. Form a pointer for the base. */
@@ -139,6 +140,8 @@
    return false;
 }

+struct mutex spi_dma_hw_mutex;
+
 static ssize_t spi_dma_readat_dma(const struct region_device *rd, void *b, size_t offset,
    			  size_t size)
 {
@@ -152,12 +155,16 @@
    printk(BIOS_SPEW, "%s: start: dest: %p, offset: %#zx, size: %zu\n", __func__, b, offset,
           size);

+	mutex_lock(&spi_dma_hw_mutex);
+
    start_spi_dma_transaction(&transaction);

do {
    	udelay(10);
    } while (continue_spi_dma_transaction(rd, &transaction));

+	mutex_unlock(&spi_dma_hw_mutex);
+
    printk(BIOS_SPEW, "%s: end: dest: %p, offset: %#zx, size: %zu, remaining: %zu\n",
           __func__, b, offset, size, transaction.remaining);