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From:   Ulf Hansson <ulf.hansson@linaro.org>
Date:   Wed, 13 Feb 2019 08:24:33 +0100
Message-ID: <CAPDyKFpL9DT_JUgWe9ZeOSro9vQ-xh9TnpP3zkRxJ8pb=0jyXg@mail.gmail.com>
Subject: Re: [PATCH] mmc: mmc: Fix HS setting in mmc_hs400_to_hs200()
To:     Chaotian Jing <chaotian.jing@mediatek.com>
Cc:     Adrian Hunter <adrian.hunter@intel.com>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        Shawn Lin <shawn.lin@rock-chips.com>,
        Simon Horman <horms+renesas@verge.net.au>,
        Kyle Roeschley <kyle.roeschley@ni.com>,
        Hongjie Fang <hongjiefang@asrmicro.com>,
        Harish Jenny K N <harish_kandiga@mentor.com>,
        "linux-mmc@vger.kernel.org" <linux-mmc@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        linux-mediatek@lists.infradead.org,
        srv_heupstream <srv_heupstream@mediatek.com>
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On Wed, 13 Feb 2019 at 04:13, Chaotian Jing <chaotian.jing@mediatek.com> wrote:
>
> On Wed, 2019-02-13 at 08:54 +0800, Chaotian Jing wrote:
> > On Tue, 2019-02-12 at 10:04 +0200, Adrian Hunter wrote:
> > > On 12/02/19 4:04 AM, Chaotian Jing wrote:
> > > > On Tue, 2019-02-05 at 15:42 +0200, Adrian Hunter wrote:
> > > >> On 5/02/19 3:06 PM, Ulf Hansson wrote:
> > > >>> On Mon, 4 Feb 2019 at 14:42, Adrian Hunter <adrian.hunter@intel.com> wrote:
> > > >>>>
> > > >>>> On 4/02/19 12:54 PM, Ulf Hansson wrote:
> > > >>>>> On Mon, 4 Feb 2019 at 10:58, Adrian Hunter <adrian.hunter@intel.com> wrote:
> > > >>>>>>
> > > >>>>>> On 1/02/19 10:10 AM, Ulf Hansson wrote:
> > > >>>>>>> On Fri, 1 Feb 2019 at 02:38, Chaotian Jing <chaotian.jing@mediatek.com> wrote:
> > > >>>>>>>>
> > > >>>>>>>> On Thu, 2019-01-31 at 16:58 +0100, Ulf Hansson wrote:
> > > >>>>>>>>> On Thu, 31 Jan 2019 at 08:53, Chaotian Jing <chaotian.jing@mediatek.com> wrote:
> > > >>>>>>>>>>
> > > >>>>>>>>>> mmc_hs400_to_hs200() begins with the card and host in HS400 mode.
> > > >>>>>>>>>> Therefore, any commands sent to the card should use HS400 timing.
> > > >>>>>>>>>> It is incorrect to reduce frequency to 50Mhz before sending the switch
> > > >>>>>>>>>> command, in this case, only reduce clock frequency to 50Mhz but without
> > > >>>>>>>>>> host timming change, host is still in hs400 mode but clock changed from
> > > >>>>>>>>>> 200Mhz to 50Mhz, which makes the tuning result unsuitable and cause
> > > >>>>>>>>>> the switch command gets response CRC error.
> > > >>>>>>>>>
> > > >>>>>>>>> According the eMMC spec there is no violation by decreasing the clock
> > > >>>>>>>>> frequency like this. We can use whatever value <=200MHz.
> > > >>>>>>>>>
> > > >>>>>>>>> However, perhaps in practice this becomes an issue, due to the tuning
> > > >>>>>>>>> for HS400 has been done on the "current" frequency.
> > > >>>>>>>>>
> > > >>>>>>>>> As as start, I think you need to clarify this in the changelog.
> > > >>>>>>>>>
> > > >>>>>>>> Yes, reduce clock frequency to 50Mhz is no Spec violation, but it may
> > > >>>>>>>> cause __mmc_switch() gets response CRC error, decreasing the clock but
> > > >>>>>>>> without HOST mode change, on the host side, host driver do not know
> > > >>>>>>>> what's operation the core layer want to do and can only set current bus
> > > >>>>>>>> clock to 50Mhz, without tuning parameter change, it has a chance lead to
> > > >>>>>>>> response CRC error. even lower clock frequency, but with the wrong
> > > >>>>>>>> tuning parameter setting(the setting is of hs400 tuning @200Mhz).
> > > >>>>>>>
> > > >>>>>>> Right, makes sense.
> > > >>>>>>>
> > > >>>>>>>>>>
> > > >>>>>>>>>> this patch refers to mmc_select_hs400(), make the reduce clock frequency
> > > >>>>>>>>>> after card timing change.
> > > >>>>>>>>>>
> > > >>>>>>>>>> Signed-off-by: Chaotian Jing <chaotian.jing@mediatek.com>
> > > >>>>>>>>>> ---
> > > >>>>>>>>>>  drivers/mmc/core/mmc.c | 8 ++++----
> > > >>>>>>>>>>  1 file changed, 4 insertions(+), 4 deletions(-)
> > > >>>>>>>>>>
> > > >>>>>>>>>> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
> > > >>>>>>>>>> index da892a5..21b811e 100644
> > > >>>>>>>>>> --- a/drivers/mmc/core/mmc.c
> > > >>>>>>>>>> +++ b/drivers/mmc/core/mmc.c
> > > >>>>>>>>>> @@ -1239,10 +1239,6 @@ int mmc_hs400_to_hs200(struct mmc_card *card)
> > > >>>>>>>>>>         int err;
> > > >>>>>>>>>>         u8 val;
> > > >>>>>>>>>>
> > > >>>>>>>>>> -       /* Reduce frequency to HS */
> > > >>>>>>>>>> -       max_dtr = card->ext_csd.hs_max_dtr;
> > > >>>>>>>>>> -       mmc_set_clock(host, max_dtr);
> > > >>>>>>>>>> -
> > > >>>>>>>>>
> > > >>>>>>>>> As far as I can tell, the reason to why we change the clock frequency
> > > >>>>>>>>> *before* the call to __mmc_switch() below, is probably to try to be on
> > > >>>>>>>>> the safe side and conform to the spec.
> > > >>>>>>>>>
> > > >>>>>>>> Agree, it Must be more safe with lower clock frequency, but the
> > > >>>>>>>> precondition is to make the host side recognize current timing is not
> > > >>>>>>>> HS400 mode. it has no method to find a safe setting to ensure no
> > > >>>>>>>> response CRC error when reduce clock from 200Mhz to 50Mhz.
> > > >>>>>>>>> However, I think you have a point, as the call to __mmc_switch(),
> > > >>>>>>>>> passes the "send_status" parameter as false, no other command than the
> > > >>>>>>>>> CMD6 is sent to the card.
> > > >>>>>>>>>
> > > >>>>>>>> yes, the send status command was sent only after __mmc_switch() done.
> > > >>>>>>>>>>         /* Switch HS400 to HS DDR */
> > > >>>>>>>>>>         val = EXT_CSD_TIMING_HS;
> > > >>>>>>>>>>         err = __mmc_switch(card, EXT_CSD_CMD_SET_NORMAL, EXT_CSD_HS_TIMING,
> > > >>>>>>>>>> @@ -1253,6 +1249,10 @@ int mmc_hs400_to_hs200(struct mmc_card *card)
> > > >>>>>>>>>>
> > > >>>>>>>>>>         mmc_set_timing(host, MMC_TIMING_MMC_DDR52);
> > > >>>>>>>>>>
> > > >>>>>>>>>> +       /* Reduce frequency to HS */
> > > >>>>>>>>>> +       max_dtr = card->ext_csd.hs_max_dtr;
> > > >>>>>>>>>> +       mmc_set_clock(host, max_dtr);
> > > >>>>>>>>>> +
> > > >>>>>>>>>
> > > >>>>>>>>> Perhaps it's even more correct to change the clock frequency before
> > > >>>>>>>>> the call to mmc_set_timing(host, MMC_TIMING_MMC_DDR52). Otherwise you
> > > >>>>>>>>> will be using the DDR52 timing in the controller, but with a too high
> > > >>>>>>>>> frequency.
> > > >>>>>>>>>
> > > >>>>>>>> for Our host, it has no impact to change the clock before or after
> > > >>>>>>>> change timing, as the mmc_set_timing() is only for host side, not
> > > >>>>>>>> related to MMC card side and no commands sent do card before the
> > > >>>>>>>> timing/clock change completed.
> > > >>>>>>>
> > > >>>>>>> Alright. After a second thought, it actually looks more consistent
> > > >>>>>>> with mmc_select_hs400() to do it after, as what you propose in
> > > >>>>>>> $subject patch.
> > > >>>>>>>
> > > >>>>>>> So, let's keep it as is.
> > > >>>>>>>
> > > >>>>>>>>>>         err = mmc_switch_status(card);
> > > >>>>>>>>>>         if (err)
> > > >>>>>>>>>>                 goto out_err;
> > > >>>>>>>>>> --
> > > >>>>>>>>>> 1.8.1.1.dirty
> > > >>>>>>>>>>
> > > >>>>>>>>>
> > > >>>>>>>>> Finally, it sounds like you are trying to fix a real problem, can you
> > > >>>>>>>>> please provide some more information what is happening when the
> > > >>>>>>>>> problem occurs at your side?
> > > >>>>>>>>>
> > > >>>>>>>> Yes, I got a problem with new kernel version. with
> > > >>>>>>>> commit:57da0c042f4af52614f4bd1a148155a299ae5cd8, this commit makes
> > > >>>>>>>> re-tuning every time when access RPMB partition.
> > > >>>>>>>
> > > >>>>>>> Okay, could you please add this as fixes tag for the next version of the patch.
> > > >>>>>>>
> > > > Ok, sorry for late reply due to Chinese New Year.
> > > >>>>>>>>
> > > >>>>>>>> in fact, our host tuning result of hs400 is very stable and almost never
> > > >>>>>>>> get response CRC error with clock frequency at 200Mhz. but cannot ensure
> > > >>>>>>>> this tuning result also suitable when running at HS400 mode @50Mhz. as I
> > > >>>>>>>> mentioned before, the host side does not know the reason of reduce clock
> > > >>>>>>>> frequency to 50Mhz at HS400 mode, so what's the host side can do is only
> > > >>>>>>>> reduce the bus clock to 50Mhz, even it can just only set the tuning
> > > >>>>>>>> setting to default when clock frequency lower than 50Mhz, but both card
> > > >>>>>>>> & host side are still at HS400 mode, still cannot ensure this setting is
> > > >>>>>>>> suitable.
> > > >>>>>>>
> > > >>>>>>> Right, thanks for clarifying.
> > > >>>>>>>
> > > >>>>>>> So I am expecting a new version with a fixes tag and some
> > > >>>>>>> clarification of the changelog, then I am ready to apply this to give
> > > >>>>>>> it some test.
> > > >>>>>>
> > > >>>>>> The switch from HS400 mode is done for tuning at times when CRC errors are a
> > > >>>>>> possibility e.g. after a CRC error during transfer.  So if the frequency is
> > > >>>>>> not to be reduced, then some mitigation is needed for the possibility that
> > > >>>>>> the CMD6 response itself will have a CRC error.
> > > >>>>>
> > > >>>>> That's a good point!
> > > >>>>>
> > > >>>>> However, how can we know that a CMD6 command is successfully
> > > >>>>> completed, if there is CRC errors detected during the transmission? I
> > > >>>>> guess we can't!?
> > > >>>>
> > > >>>> Yes, in that case, the only option is to assume the CMD6 was successful,
> > > >>>> like in
> > > >>>>
> > > >>>>   commit ef3d232245ab7a1bf361c52449e612e4c8b7c5ab
> > > >>>>   Author: Adrian Hunter <adrian.hunter@intel.com>
> > > >>>>   Date:   Fri Dec 2 13:16:35 2016 +0200
> > > >>>>
> > > >>>>       mmc: mmc: Relax checking for switch errors after HS200 switch
> > > >>>
> > > >>> Well, relaxing the check for switch errors, is to me a different
> > > >>> thing. This means we are first doing the CMD6, then allowing the
> > > >>> following status command (CMD13) to have CRC errors. Actually, even
> > > >>> the spec mention this as a case to consider. I guess it's because the
> > > >>> card internally have switched to a new speed mode timing.
> > > >>>
> > > >>> Allowing CRC errors for the actual CMD6 sound more fragile to me. Of
> > > >>> course, we can always try and see what happens.
> > > >>>
> > > >>> Chaotian, can you give it a go? Somehow, change the call to
> > > >>> __mmc_switch() in mmc_hs400_to_hs200(), so the CMD6 doesn't have the
> > > >>> CRC flag set.
> @Adrian, @Ulf, another question: if remove the MMC_RSP_CRC flag, it will
> have big impact to all host driver, as the "mmc_resp_type()" can not get
> MMC_RESP_R1B return value, so many host drivers use mmc_resp_type() to
> get resp type. if We make CMD6 does not have CRC flag set, then We must
> modify the using of "mmc_resp_type()" to "mmc_resp_type() | MMC_RSP_CRC"
> in all host drives. the same issue occurs at other place which remove
> MMC_RSP_CRC(eg. mmc_cqe_recovery()).

The idea is actually to try to change this for all host drivers, of
course it's only for this particular CMD6 in question, so not for all
CMD6.

However, before we consider doing such a change, we need to know if it
solves the problem for you? If it doesn't, then we can drop the idea.

As a perhaps better alternative, Adrian also suggested, if possible,
to let the mediatek driver change to "fixed sampling mode" via the
->set_ios() host ops, at the point when the clk rate drops to
HS-frequency, but still running with MMC_TIMING_MMC_HS400 timings. Of
course this means "fixed sampling" needs to be supported by the
mediatek IP.

If neither of this works for you, we need to consider something else.

[...]

Kind regards
Uffe