mmc: mmc_spi: multiple block read remove read crc ack

For multiple block read, the current implementation, transfer packet
includes cmd53 + cmd53 response + block nums*(1byte token +
block length bytes payload + 2bytes CRC + 1byte transfer), the last
1byte transfer of every block is not needed, so remove it.

Why doesn't multiple block read need CRC ack?
For read operation, host side get the payload and CRC value, then
will only check the CRC value to confirm if the data is correct or
not, but not send CRC ack to card. If the data is correct, save it,
or discard it and retransmit if data is error, so the last 1byte
transfer of every block make no sense.

What's the side effect of this 1byte transfer?
As the SPI is full duplex, if add this redundant 1byte transfer, SDIO
card side take it as the token of next block, then all the next sub
blocks sequence distort.

Signed-off-by: Rex Chen <rex.chen_1@nxp.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20250728082230.1037917-3-rex.chen_1@nxp.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

diff --git a/drivers/mmc/host/mmc_spi.c b/drivers/mmc/host/mmc_spi.c
index 35b0ad273b4ff6e7194a305cb4e63ab2a4acedb7..95a32ff29ee166602ab9d9d1dc1c6911f2f36eee 100644 (file)
--- a/drivers/mmc/host/mmc_spi.c
+++ b/drivers/mmc/host/mmc_spi.c
@@ -563,7 +563,7 @@ mmc_spi_setup_data_message(struct mmc_spi_host *host, bool multiple, bool write)
         * the next token (next data block, or STOP_TRAN).  We can try to
         * minimize I/O ops by using a single read to collect end-of-busy.
         */
-       if (multiple || write) {
+       if (write) {
                t = &host->early_status;
                memset(t, 0, sizeof(*t));
                t->len = write ? sizeof(scratch->status) : 1;