[PATCH 7/7] eeprom: at25: Split reads into chunks and cap write size

Eddie James
2020-08-20T17:03:49Z

From: Brad Bishop <bradleyb@fuzziesquirrel.com>

Make use of spi_max_transfer_size to avoid requesting transfers that are
too large for some spi controllers.

Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
Signed-off-by: Eddie James <eajames@linux.ibm.com>
Signed-off-by: Joel Stanley <joel@jms.id.au>
---
drivers/misc/eeprom/at25.c | 94 ++++++++++++++++++++++----------------
1 file changed, 54 insertions(+), 40 deletions(-)

diff --git a/drivers/misc/eeprom/at25.c b/drivers/misc/eeprom/at25.c
index ed8d38b09925..30f0704ab2d4 100644
--- a/drivers/misc/eeprom/at25.c
+++ b/drivers/misc/eeprom/at25.c
@@ -64,12 +64,17 @@ static int at25_ee_read(void *priv, unsigned int offset,
{
struct at25_data *at25 = priv;
char *buf = val;
+ size_t max_chunk = spi_max_transfer_size(at25->spi);
+ size_t num_msgs = DIV_ROUND_UP(count, max_chunk);
+ size_t nr_bytes = 0;
u8 command[EE_MAXADDRLEN + 1];
u8 *cp;
ssize_t status;
struct spi_transfer t[2];
struct spi_message m;
u8 instr;
+ unsigned int msg_offset;
+ size_t msg_count;

if (unlikely(offset >= at25->chip.byte_len))
return -EINVAL;
@@ -78,57 +83,64 @@ static int at25_ee_read(void *priv, unsigned int offset,
if (unlikely(!count))
return -EINVAL;

- cp = command;
-
- instr = AT25_READ;
- if (at25->chip.flags & EE_INSTR_BIT3_IS_ADDR)
- if (offset >= (1U << (at25->addrlen * 8)))
- instr |= AT25_INSTR_BIT3;
- *cp++ = instr;
-
- /* 8/16/24-bit address is written MSB first */
- switch (at25->addrlen) {
- default: /* case 3 */
- *cp++ = offset >> 16;
- fallthrough;
- case 2:
- *cp++ = offset >> 8;
- fallthrough;
- case 1:
- case 0: /* can't happen: for better codegen */
- *cp++ = offset >> 0;
- }
+ msg_offset = (unsigned int)offset;
+ msg_count = min(count, max_chunk);
+ while (num_msgs) {
+ cp = command;
+
+ instr = AT25_READ;
+ if (at25->chip.flags & EE_INSTR_BIT3_IS_ADDR)
+ if (msg_offset >= (1U << (at25->addrlen * 8)))
+ instr |= AT25_INSTR_BIT3;
+ *cp++ = instr;
+
+ /* 8/16/24-bit address is written MSB first */
+ switch (at25->addrlen) {
+ default: /* case 3 */
+ *cp++ = msg_offset >> 16;
+ fallthrough;
+ case 2:
+ *cp++ = msg_offset >> 8;
+ fallthrough;
+ case 1:
+ case 0: /* can't happen: for better codegen */
+ *cp++ = msg_offset >> 0;
+ }

- spi_message_init(&m);
- memset(t, 0, sizeof(t));
+ spi_message_init(&m);
+ memset(t, 0, sizeof(t));

- t[0].tx_buf = command;
- t[0].len = at25->addrlen + 1;
- spi_message_add_tail(&t[0], &m);
+ t[0].tx_buf = command;
+ t[0].len = at25->addrlen + 1;
+ spi_message_add_tail(&t[0], &m);

- t[1].rx_buf = buf;
- t[1].len = count;
- spi_message_add_tail(&t[1], &m);
+ t[1].rx_buf = buf + nr_bytes;
+ t[1].len = msg_count;
+ spi_message_add_tail(&t[1], &m);

- mutex_lock(&at25->lock);
+ mutex_lock(&at25->lock);

- /* Read it all at once.
- *
- * REVISIT that's potentially a problem with large chips, if
- * other devices on the bus need to be accessed regularly or
- * this chip is clocked very slowly
- */
- status = spi_sync(at25->spi, &m);
- dev_dbg(&at25->spi->dev, "read %zu bytes at %d --> %zd\n",
- count, offset, status);
+ status = spi_sync(at25->spi, &m);

- mutex_unlock(&at25->lock);
- return status;
+ mutex_unlock(&at25->lock);
+
+ if (status)
+ return status;
+
+ --num_msgs;
+ msg_offset += msg_count;
+ nr_bytes += msg_count;
+ }
+
+ dev_dbg(&at25->spi->dev, "read %zu bytes at %d\n",
+ count, offset);
+ return 0;
}

static int at25_ee_write(void *priv, unsigned int off, void *val, size_t count)
{
struct at25_data *at25 = priv;
+ size_t maxsz = spi_max_transfer_size(at25->spi);
const char *buf = val;
int status = 0;
unsigned buf_size;
@@ -191,6 +203,8 @@ static int at25_ee_write(void *priv, unsigned int off, void *val, size_t count)
segment = buf_size - (offset % buf_size);
if (segment > count)
segment = count;
+ if (segment > maxsz)
+ segment = maxsz;
memcpy(cp, buf, segment);
status = spi_write(at25->spi, bounce,
segment + at25->addrlen + 1);
--
2.26.2