From: Ulf Hansson <ulf.hansson@linaro.org>
To: Chaotian Jing <chaotian.jing@mediatek.com>
Cc: srv_heupstream <srv_heupstream@mediatek.com>,
Shawn Lin <shawn.lin@rock-chips.com>,
"linux-mmc@vger.kernel.org" <linux-mmc@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-mediatek@lists.infradead.org,
Harish Jenny K N <harish_kandiga@mentor.com>,
Hongjie Fang <hongjiefang@asrmicro.com>,
Matthias Brugger <matthias.bgg@gmail.com>,
Simon Horman <horms+renesas@verge.net.au>,
Kyle Roeschley <kyle.roeschley@ni.com>,
Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH] mmc: mmc: Fix HS setting in mmc_hs400_to_hs200()
Date: Thu, 31 Jan 2019 16:58:06 +0100 [thread overview]
Message-ID: <CAPDyKFruCCs_un1oR-gd1P=ZGryyHwKuY0SkvLO2=Jm1bGV6sQ@mail.gmail.com> (raw)
In-Reply-To: <1548921212-5219-1-git-send-email-chaotian.jing@mediatek.com>
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.
>
> 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.
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.
> /* 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.
> 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?
Kind regards
Uffe
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next prev parent reply other threads:[~2019-01-31 15:58 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-31 7:53 [PATCH] mmc: mmc: Fix HS setting in mmc_hs400_to_hs200() Chaotian Jing
2019-01-31 15:58 ` Ulf Hansson [this message]
2019-02-01 1:38 ` Chaotian Jing
2019-02-01 8:10 ` Ulf Hansson
2019-02-04 9:56 ` Adrian Hunter
2019-02-04 10:54 ` Ulf Hansson
2019-02-04 13:40 ` Adrian Hunter
2019-02-05 13:06 ` Ulf Hansson
2019-02-05 13:42 ` Adrian Hunter
2019-02-12 2:04 ` Chaotian Jing
2019-02-12 8:04 ` Adrian Hunter
2019-02-13 0:54 ` Chaotian Jing
2019-02-13 3:13 ` Chaotian Jing
2019-02-13 7:24 ` Ulf Hansson
2019-02-13 7:55 ` Chaotian Jing
2019-02-13 8:33 ` Ulf Hansson
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