On 2019/3/6 16:48, Ulf Hansson wrote:
On Wed, 6 Mar 2019 at 01:45, Shawn Lin <shawn.lin@xxxxxxxxxxxxxx> wrote:
Hi Ulf
On 2019/3/5 17:31, Ulf Hansson wrote:
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?
I haven't talked with HW designers from device vendors.
You don't need to card vendors, but your own HW guys that develops
your mmc controller. But, I assume you have done that, just wanted to
confirm it!?
yes, I did.
The point is, that you are referring to the JEDEC spec in the
changelog, which in the end doesn't described the internal specific
behavior of your mmc controller. Perhaps you could clarify that in the
next version of the changelog.
(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?
I don't get your point. What I mean is to skip doing memcmp but not
checking whether or why memcmp failed after calling mmc_send_tuning().
I was just looking at mtk-sd, which sometimes seems to care about
whether the memcmp fails, while in others it doesn't. Honestly, I
don't recall why so.
Now, if we add a host cap, along the lines of what you propose, mtk-sd
may not be able to use it, as it means the memcmp will always be
skipped.
The whole point is if the controller has the HW capability to check
the tuning block, so data->error in mmc_send_tuning will let mmc core
know if it need to manually compare the raw tuning block data.
Right, so to be clear, this works for me as well! I just wanted to
raise the idea above, with using a specific error code.
However, may I suggest "MMC_CAP2_HW_TUNING" instead of
MMC_CAP2_NO_TUNING_CMP, as to try to better describe the behavior of
the HW?
Also, if I am going to pick a patch adding this new cap, I would also
like to get at least one mmc host that use it, so please add a patch
on top for that.
Ok, I got it.
[...]
Kind regards
Uffe
