This caps2 is to skip doing memory compare tuning block
pattern with the received data from devices when doing
tuning.
The data from device is all formatted like:
Start bit + data + CRC + End bit
For normal data read, we just verify host sample the data
w/o any errors, but not need care the data context. But for
a tuning process, we now compare the data context with JEDEC
pattern. I highly suspect the rational behide it for the following
details:
(1) The tuning process is mostly used for identifing the rational
sample window, so if the host read the tuning block successfully
like a noraml data read, isn't it enough for sure that *this* single
sample phase is good to work, no? The original patch to support it
didn't quote any spec details but let's see the JESD84-B51, section 6.6.5,
"Bus Sampling Tuning Concept" just says "This example is given for
concept explanation purpose. The Host may use any other implementation
according to its design consideration. " The concept isn't the order,
and whether the MMC core need to verify the tuning block? See my argue (2).
(2) AFAICT, the tuning block is handled by a fixed HW module within
the device, if a JEDEC compatible device receive tuning block cmd and
response it, could it sends back a non-compatible tuning block?
(3) Some(it's impossible for me to check all) of the SDHCI IP instances
at hand which do tuning by HW block,never check the tuning block at all.
I'm intended to remove it entirely but just stay back a bit for
skipping that if any vendors are willing to try(At least rockchip does).
Any comments will be appreciated.
Signed-off-by: Shawn Lin <shawn.lin@xxxxxxxxxxxxxx>
---
drivers/mmc/core/mmc_ops.c | 3 ++-
include/linux/mmc/host.h | 1 +
2 files changed, 3 insertions(+), 1 deletion(-)
diff --git a/drivers/mmc/core/mmc_ops.c b/drivers/mmc/core/mmc_ops.c
index c5208fb..802cba5 100644
--- a/drivers/mmc/core/mmc_ops.c
+++ b/drivers/mmc/core/mmc_ops.c
@@ -664,7 +664,8 @@ int mmc_send_tuning(struct mmc_host *host, u32 opcode, int *cmd_error)
goto out;
}
- if (memcmp(data_buf, tuning_block_pattern, size))
+ if (!(host->caps & MMC_CAP2_NO_TUNING_CMP) &&
+ memcmp(data_buf, tuning_block_pattern, size))
err = -EIO;
out:
diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
index 43d0f0c..8e759ff 100644
--- a/include/linux/mmc/host.h
+++ b/include/linux/mmc/host.h
@@ -370,6 +370,7 @@ struct mmc_host {
#define MMC_CAP2_CQE (1 << 23) /* Has eMMC command queue engine */
#define MMC_CAP2_CQE_DCMD (1 << 24) /* CQE can issue a direct command */
#define MMC_CAP2_AVOID_3_3V (1 << 25) /* Host must negotiate down from 3.3V */
+#define MMC_CAP2_NO_TUNING_CMP (1 << 25) /* Do not need compare the tuning block */
int fixed_drv_type; /* fixed driver type for non-removable media */
--
1.9.1
