linux_spi: Dynamically detect max buffer size

Read max buffer size from sysfs if available.

Change-Id: Ic541e548ced8488f074d388f1c92174cad123064
Signed-off-by: Keno Fischer <keno@juliacomputing.com>
Signed-off-by: David Hendricks <dhendricks@fb.com>
Reviewed-on: https://review.coreboot.org/22441
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>

1 files changed, 45 insertions, 7 deletions

diff --git a/linux_spi.c b/linux_spi.c
index e51fbc420..611559ac0 100644
--- a/linux_spi.c
+++ b/linux_spi.c
@@ -42,6 +42,8 @@
  */
 
 static int fd = -1;
+#define BUF_SIZE_FROM_SYSFS	"/sys/module/spidev/parameters/bufsiz"
+static size_t max_kernel_buf_size;
 
 static int linux_spi_shutdown(void *data);
 static int linux_spi_send_command(struct flashctx *flash, unsigned int writecnt,
@@ -127,8 +129,45 @@ int linux_spi_init(void)
 		return 1;
 	}
 
-	register_spi_master(&spi_master_linux);
+	/* Read max buffer size from sysfs, or use page size as fallback. */
+	FILE *fp;
+	fp = fopen(BUF_SIZE_FROM_SYSFS, "r");
+	if (!fp) {
+		msg_pwarn("Cannot open %s: %s.\n", BUF_SIZE_FROM_SYSFS, strerror(errno));
+		goto out;
+	}
+
+	char buf[10];
+	memset(buf, 0, sizeof(buf));
+	if (!fread(buf, 1, sizeof(buf) - 1, fp)) {
+		if (feof(fp))
+			msg_pwarn("Cannot read %s: file is empty.\n", BUF_SIZE_FROM_SYSFS);
+		else
+			msg_pwarn("Cannot read %s: %s.\n", BUF_SIZE_FROM_SYSFS, strerror(errno));
+		goto out;
+	}
+
+	long int tmp;
+	errno = 0;
+	tmp = strtol(buf, NULL, 0);
+	if ((tmp < 0) || errno) {
+		msg_pwarn("Buffer size %ld from %s seems wrong.\n", tmp, BUF_SIZE_FROM_SYSFS);
+	} else {
+		msg_pdbg("%s: Using value from %s as max buffer size.\n", __func__, BUF_SIZE_FROM_SYSFS);
+		max_kernel_buf_size = (size_t)tmp;
+	}
 
+out:
+	if (fp)
+		fclose(fp);
+
+	if (!max_kernel_buf_size) {
+		msg_pdbg("%s: Using page size as max buffer size.\n", __func__);
+		max_kernel_buf_size = (size_t)getpagesize();
+	}
+
+	msg_pdbg("%s: max_kernel_buf_size: %zu\n", __func__, max_kernel_buf_size);
+	register_spi_master(&spi_master_linux);
 	return 0;
 }
 
@@ -179,17 +218,16 @@ static int linux_spi_send_command(struct flashctx *flash, unsigned int writecnt,
 	return 0;
 }
 
-static int linux_spi_read(struct flashctx *flash, uint8_t *buf,
-			  unsigned int start, unsigned int len)
+static int linux_spi_read(struct flashctx *flash, uint8_t *buf, unsigned int start, unsigned int len)
 {
-	return spi_read_chunked(flash, buf, start, len,
-				(unsigned int)getpagesize());
+	/* Read buffer is fully utilized for data. */
+	return spi_read_chunked(flash, buf, start, len, max_kernel_buf_size);
 }
 
 static int linux_spi_write_256(struct flashctx *flash, const uint8_t *buf, unsigned int start, unsigned int len)
 {
-	return spi_write_chunked(flash, buf, start, len,
-				((unsigned int)getpagesize()) - 4);
+	/* 5 bytes must be reserved for longest possible command + address. */
+	return spi_write_chunked(flash, buf, start, len, max_kernel_buf_size - 5);
 }
 
 #endif // CONFIG_LINUX_SPI == 1