Re: [PATCH 1/2] mmc: core: use card pointer as the first parameter of execute_tuning()

[Jaehoon Chung <jh80.chung@samsung.com>]

On 01/30/2015 09:13 AM, Doug Anderson wrote:
> Ulf,
> 
> On Thu, Jan 29, 2015 at 1:16 AM, Ulf Hansson <ulf.hansson@linaro.org> wrote:
>> - Drastically decreased cc-list.
>>
>> On 29 January 2015 at 01:55, Doug Anderson <dianders@chromium.org> wrote:
>>> Ulf,
>>>
>>> On Tue, Jan 27, 2015 at 7:18 AM, Ulf Hansson <ulf.hansson@linaro.org> wrote:
>>>>> I asked Addy to post upstream against mmc_send_tuning(), but I guess
>>>>> he didn't (he posted against Alex's NAKed patch instead).
>>>>>
>>>>> ...when I talked to him about it, Addy was asserting that when tuning
>>>>> fails it is important (at least on dw_mmc on rk3288) that we wait for
>>>>> the card to stop being busy and that the way to detect was using
>>>>> mmc_send_status().
>>>>
>>>> So, could that be due to the internal logic of the error handling in
>>>> dw_mmc driver? Or you think this is a generic issue?
>>>>
>>>> According to the specifications (eMMC and SD) both states that the
>>>> tuning command has an R1 response. So, there shouldn't be any busy
>>>> signalling involved - at least according to spec.
>>>
>>> I did a bit of digging into this issue myself.  What I found was that
>>> a "response CRC" and "end of transfer".  This was why I posted up
>>> <https://patchwork.kernel.org/patch/5623071/>.  From that patch:
>>>
>>>> Specifically it looks like in certain error conditions (I saw this
>>>> with Response CRC errors) that data keeps showing up in the FIFO even
>>>> after the error is reported and the CD (command done) bit is set.  If
>>>> we don't wait for this data to finish transferring then it confuses
>>>> the next transaction.  In the specific failure case I ran into I found
>>>> that I could monitor the data_state_mc_busy bit and wait for it to
>>>> clear, but in other failure cases this bit was stuck at busy when we
>>>> saw an error.  Hence a generic big delay seems like the only option.
>>
>> I haven't queued that patch, I was waiting for an ack from Seungwon or Jaehoon.

Sorry, which patch? i missed it.

>>
>> Do you think it could solve this issue, we could give it a try!?
> 
> My big fat delay does seem to solve the issue, but it has the side
> effect of slowing down tuning quite a bit so I'd rather find a more
> proper fix.  We're talking several hundred extra milliseconds slower
> per slot that is tuned...
> 
> I still don't exactly have a warm fuzzy about using the send_status()
> command like this, but it seems to work (actually, I should verify
> that myself--I've been taking Addy's word that his solution works).  I
> do wish someone could tell me "oh right, yeah, we do need a
> send_status in that case".  ;)  Addy said that in the non-tuning case
> that the core will always do a send_status so that this fix is really
> only for tuning and doesn't need to be applied in general.  I also
> haven't validated that myself...
> 
> Overall it does sorta seem like this might just be a quirk with the
> rk3288 dw_mmc.  It feels like the controller is in a wonky state and
> maybe this extra send_status helps it get out?

I think that dw-mmc controller seems to have the main problem for tuning sequence.
In my knowledge, tuning sequence doesn't need to send the stop command.
but the code of dw-mmc need to handle the stop command and it has implemented.
Using Send_status() is good solution, but i think it's not main solution.

I will work to clean up the code for dwmmc controller.
And consider to handle the stop command..

Best Regards,
Jaehoon Chung
> 
> 
>>> ...Addy instead fixed the problem using mmc_send_status() to try to
>>> detect when the transfer was all done and it apparently worked, but it
>>> seemed odd to me.  My MMC "expertise" pretty much ends with looking
>>> for simple logic errors in the MMC driver, so my hope was that one of
>>> you guys would know this better...
>>>
>>>
>>>>> That would mean that against upstream you'd need to change
>>>>> mmc_send_tuning() to take in the card as well (or move the "host->card
>>>>> = card" assignment to before UHS init, which seems less desirable?)
>>
>> I get your point now.
>>
>> Changing mmc_send_tuning() to take "card" will work due to $subject
>> patch changed the ->execute_tuning() callbacks to take "card" as well.
>>
>>>>>
>>>>> What do you think about that?  Is there a better solution?
>>>>
>>>> Why do we need to change mmc_send_tuning()? I thought the issue was
>>>> that mmc_send_status(), which currently takes "card" as a parameter.
>>>
>>> Well, if mmc_send_tuning() needed to call mmc_send_status() then
>>> mmc_send_tuning() would need the card parameter, right?
>>
>> Correct, got it now. :-)
>>
>> I didn't understand that you wanted mmc_send_tuning() to invoke
>> mmc_send_status() while it got some errors. From Addy's patch2,
>> mmc_send_status() is invoked from the host driver.
>>
>> Anyway, I think we should follow your suggestion to change the
>> behaviour of mmc_send_tuning(). Though, I think it should use
>> bus_ops->alive() callback instead (and that callback then also need to
>> change to take "card" as a parameter), since that would be generic and
>> the cover the SDIO case as well.
> 
> That sounds reasonable to me.
> 
> Addy: you've been very quiet.  What do you think?
> 
> -Doug
>