Change in flashrom[master]: linux_spi: Reduce maximum read chunksize

[Nico Huber (Code Review)]

Nico Huber has submitted this change and it was merged. ( https://review.coreboot.org/25149 )

Change subject: linux_spi: Reduce maximum read chunksize
......................................................................

linux_spi: Reduce maximum read chunksize

It turned out that older kernels use a single buffer of `bufsiz` bytes
for combined input and output data. So we have to account for the read
command + max 4 address bytes.

Change-Id: Ide50db38af1004fde09a70b15938e77f5e1285ac
Signed-off-by: Nico Huber 
Tested-by: Julian von Mendel 
Reviewed-on: https://review.coreboot.org/25149
Tested-by: build bot (Jenkins) 
Reviewed-by: Julian von Mendel 
Reviewed-by: David Hendricks 
---
M linux_spi.c
1 file changed, 3 insertions(+), 2 deletions(-)

Approvals:
  build bot (Jenkins): Verified
  David Hendricks: Looks good to me, approved
  Julian von Mendel: Looks good to me, but someone else must approve

diff --git a/linux_spi.c b/linux_spi.c
index 1d3605a..714e612 100644
--- a/linux_spi.c
+++ b/linux_spi.c
@@ -221,8 +221,9 @@

static int linux_spi_read(struct flashctx *flash, uint8_t *buf, unsigned int start, unsigned int len)
 {
-	/* Read buffer is fully utilized for data. */
-	return spi_read_chunked(flash, buf, start, len, max_kernel_buf_size);
+	/* Older kernels use a single buffer for combined input and output
+	   data. So account for longest possible command + address, too. */
+	return spi_read_chunked(flash, buf, start, len, max_kernel_buf_size - 5);
 }

static int linux_spi_write_256(struct flashctx *flash, const uint8_t *buf, unsigned int start, unsigned int len)