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Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1gqeVt-0008De-DC; Mon, 04 Feb 2019 13:42:17 +0000 Received: from mga07.intel.com ([134.134.136.100]) by bombadil.infradead.org with esmtps (Exim 4.90_1 #2 (Red Hat Linux)) id 1gqeVl-00089I-R8; Mon, 04 Feb 2019 13:42:15 +0000 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga005.fm.intel.com ([10.253.24.32]) by orsmga105.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 04 Feb 2019 05:42:08 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.56,560,1539673200"; d="scan'208";a="317501690" Received: from ahunter-desktop.fi.intel.com (HELO [10.237.72.56]) ([10.237.72.56]) by fmsmga005.fm.intel.com with ESMTP; 04 Feb 2019 05:42:05 -0800 Subject: Re: [PATCH] mmc: mmc: Fix HS setting in mmc_hs400_to_hs200() To: Ulf Hansson References: <1548921212-5219-1-git-send-email-chaotian.jing@mediatek.com> <1548985091.10251.26.camel@mhfsdcap03> <0e95e1a1-843e-38ea-c4bb-e6c48432ea7c@intel.com> From: Adrian Hunter Organization: Intel Finland Oy, Registered Address: PL 281, 00181 Helsinki, Business Identity Code: 0357606 - 4, Domiciled in Helsinki Message-ID: Date: Mon, 4 Feb 2019 15:40:29 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190204_054209_934781_87EDCCF6 X-CRM114-Status: GOOD ( 30.04 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: srv_heupstream , Shawn Lin , "linux-mmc@vger.kernel.org" , Linux Kernel Mailing List , linux-mediatek@lists.infradead.org, Harish Jenny K N , Linux ARM , Hongjie Fang , Matthias Brugger , Simon Horman , Kyle Roeschley , Chaotian Jing Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org Archived-At: List-Archive: On 4/02/19 12:54 PM, Ulf Hansson wrote: > On Mon, 4 Feb 2019 at 10:58, Adrian Hunter wrote: >> >> On 1/02/19 10:10 AM, Ulf Hansson wrote: >>> On Fri, 1 Feb 2019 at 02:38, Chaotian Jing wrote: >>>> >>>> On Thu, 2019-01-31 at 16:58 +0100, Ulf Hansson wrote: >>>>> On Thu, 31 Jan 2019 at 08:53, Chaotian Jing 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 >>>>>> --- >>>>>> 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. >>> >>>> >>>> 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 Date: Fri Dec 2 13:16:35 2016 +0200 mmc: mmc: Relax checking for switch errors after HS200 switch If we are going to do that, then we could stick with lowering the frequency first. Also I wonder if the mediatek driver could change to fixed sampling in ->set_ios() when the frequency drops for HS400 mode? _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel