[coreboot-gerrit] Change in coreboot[master]: soc/amd/common/block: Make SPI DMA readat co-op friendly

[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/+/56267 )

Change subject: soc/amd/common/block: Make SPI DMA readat co-op friendly
......................................................................

soc/amd/common/block: Make SPI DMA readat co-op friendly

We need to make the SPI readat method yield frequently so that we don't
block the main thread of execution for too long.

BUG=b:179699789
TEST=Boot guybrush to the OS.

Signed-off-by: Raul E Rangel 
Change-Id: Id3ec58a2e35e744b5bc2062ae479917f7f57bae9
---
M src/soc/amd/common/block/lpc/spi_dma.c
1 file changed, 21 insertions(+), 2 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/67/56267/1

diff --git a/src/soc/amd/common/block/lpc/spi_dma.c b/src/soc/amd/common/block/lpc/spi_dma.c
index dede449..9b17a38 100644
--- a/src/soc/amd/common/block/lpc/spi_dma.c
+++ b/src/soc/amd/common/block/lpc/spi_dma.c
@@ -41,14 +41,33 @@
    return 0;
 }

-static ssize_t spi_dma_readat_mmap(const struct region_device *rd, void *b, size_t offset,
+static ssize_t spi_dma_readat_mmap(const struct region_device *rd, uint8_t *b, size_t offset,
    			   size_t size)
 {
    const struct mem_region_device *mdev;
+	/*
+	 * Transfer at most 128 bytes at a time to not block too long. Otherwise
+	 * we can drastically affect the udelay timings and timestamp accounting
+	 * for other components.
+	 */
+	const size_t block_size = 128;
+	size_t remaining = size;
+	size_t transfer_size;

mdev = container_of(rd, __typeof__(*mdev), rdev);

-	memcpy(b, &mdev->base[offset], size);
+	while (remaining) {
+		transfer_size = MIN(remaining, block_size);
+
+		memcpy(b, &mdev->base[offset], transfer_size);
+
+		b += transfer_size;
+		offset += transfer_size;
+		remaining -= transfer_size;
+
+		/* Yield execution to other threads */
+		udelay(0);
+	}

return size;
 }