On Fri, 1 Mar 2019 at 08:58, Shawn Lin <shawn.lin@xxxxxxxxxxxxxx> wrote:
>
> 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?
It's hard to tell whether the above makes sense. I think only the HW
designers can give us a good answer on this, have you talked with
someone that can confirm your analyze?
>
> (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 don't think that's correct, at least by looking at the result from:
git grep -C 5 mmc_send_tuning
To me it looks like it's only mtk-sd, that in some case only checks
the cmd errors, but in others the error check also includes the memcmp
with the tuning block.
In other words, what you propose is something entirely new.
>
> 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).
An option to the host cap, could be to return a special error code,
like -EPROTO instead of -EIO as currently, in case the memcmp with the
tuning block fails.
This would allow the host to dynamically decide when it makes sense to
check for the error code, and when it doesn't.
Would that work for you?
Kind regards
Uffe
>
> 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
>
>
>
