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@xxxxxxxxx> wrote: > >> > >> On 4/02/19 12:54 PM, Ulf Hansson wrote: > >>> On Mon, 4 Feb 2019 at 10:58, Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote: > >>>> > >>>> On 1/02/19 10:10 AM, Ulf Hansson wrote: > >>>>> On Fri, 1 Feb 2019 at 02:38, Chaotian Jing <chaotian.jing@xxxxxxxxxxxx> 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@xxxxxxxxxxxx> 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@xxxxxxxxxxxx> > >>>>>>>> --- > >>>>>>>> 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@xxxxxxxxx> > >> 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. > > 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(). > >> > >> 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.
