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Subject: Re: [PATCH] mmc: mmc: Fix HS setting in mmc_hs400_to_hs200()
From:   Chaotian Jing <chaotian.jing@mediatek.com>
To:     Adrian Hunter <adrian.hunter@intel.com>
CC:     Ulf Hansson <ulf.hansson@linaro.org>,
        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>
Date:   Wed, 13 Feb 2019 11:13:14 +0800
In-Reply-To: <1550019275.16070.6.camel@mhfsdcap03>
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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()).
> > >>>
> > > Yes, but should we add a new argument of __mmc_switch(), like "bool
> > > ignore_crc" ?? for now, there are too many argument of __mmc_switch().
> > 
> > One solution for too many arguments is to make a structure to contain them. e.g.
> > 
> > struct mmc_switch_args {
> > 	u8 set;
> > 	u8 index;
> > 	u8 value;
> > 	unsigned int timeout_ms;
> > 	unsigned char timing;
> > 	bool use_busy_signal;
> > 	bool send_status;
> > 	bool retry_crc_err;
> > };
> > 
> > int __mmc_switch(struct mmc_card *card, struct mmc_switch_args *args)
> > 
> Sure, I will upload new patch to do that.
> > >>>>
> > >>>> If we are going to do that, then we could stick with lowering the frequency
> > >>>> first.
> > >>>
> > >>> Let's see what Chaotian's test may show.
> > >>>
> > >>>>
> > >>>> Also I wonder if the mediatek driver could change to fixed sampling in
> > >>>> ->set_ios() when the frequency drops for HS400 mode?
> > >>>
> > >>> Well, this sounds like a generic problem so if this is a possible
> > >>> generic solution that would be great.
> > >>>
> > >>> Is this what sdhci is doing already?
> > >>
> > >> Not at present, but some drivers seem to be adjusting their settings for
> > >> HS400 based on the frequency e.g. sdhci_msm_hs400()
> > > 
> > > It's hard to find a suitable setting for all cards when running at HS400
> > > mode @50Mhz.
> > > 
> > > 
> > 
>