From: jbrunet@baylibre.com (Jerome Brunet)
To: linus-amlogic@lists.infradead.org
Subject: mmc: UHS Voltage switch and operating frequency question
Date: Mon, 31 Jul 2017 18:20:04 +0200 [thread overview]
Message-ID: <1501518004.2759.5.camel@baylibre.com> (raw)
Hi Ulf,
I am working on adding signal voltage switch callback to the meson mmc driver.
While testing, I noticed that a few cards fail to exit the busy state after the
voltage switch.
After tinkering with the driver a bit, I noticed that increasing the clock
frequency from 400kHz to 1MHz solve the problem. Strange, isn't it ?
I'm don't know MMC that much but is it possible that some card require a minimum
operating frequency to enter UHS mode ?
The simplified spec (Part 1 - Physical Layer) says that before CMD11, we should
have had CMD41 (Init Command) . After CMD41, the card should be operating at
Default Speed or SDR12.
I believe that in both case, the frequency is "up to 25Mhz" ? This would be the
maximum, but is there a minimum ? 400kHz seems pretty low compared to 25Mhz ...
I hope you will able to shed light on this :)
Best Regards
jerome
WARNING: multiple messages have this Message-ID (diff)
From: Jerome Brunet <jbrunet@baylibre.com>
To: Ulf Hansson <ulf.hansson@linaro.org>
Cc: Kevin Hilman <khilman@baylibre.com>,
"linux-mmc@vger.kernel.org" <linux-mmc@vger.kernel.org>,
"open list:ARM/Amlogic Meson..."
<linux-amlogic@lists.infradead.org>
Subject: mmc: UHS Voltage switch and operating frequency question
Date: Mon, 31 Jul 2017 18:20:04 +0200 [thread overview]
Message-ID: <1501518004.2759.5.camel@baylibre.com> (raw)
Hi Ulf,
I am working on adding signal voltage switch callback to the meson mmc driver.
While testing, I noticed that a few cards fail to exit the busy state after the
voltage switch.
After tinkering with the driver a bit, I noticed that increasing the clock
frequency from 400kHz to 1MHz solve the problem. Strange, isn't it ?
I'm don't know MMC that much but is it possible that some card require a minimum
operating frequency to enter UHS mode ?
The simplified spec (Part 1 - Physical Layer) says that before CMD11, we should
have had CMD41 (Init Command) . After CMD41, the card should be operating at
Default Speed or SDR12.
I believe that in both case, the frequency is "up to 25Mhz" ? This would be the
maximum, but is there a minimum ? 400kHz seems pretty low compared to 25Mhz ...
I hope you will able to shed light on this :)
Best Regards
jerome
next reply other threads:[~2017-07-31 16:20 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-31 16:20 Jerome Brunet [this message]
2017-07-31 16:20 ` mmc: UHS Voltage switch and operating frequency question Jerome Brunet
2017-08-01 0:38 ` Shawn Lin
2017-08-01 0:38 ` Shawn Lin
2017-08-01 16:56 ` Jerome Brunet
2017-08-01 16:56 ` Jerome Brunet
2017-08-02 2:54 ` Shawn Lin
2017-08-02 2:54 ` Shawn Lin
2017-08-02 9:20 ` Jerome Brunet
2017-08-02 9:20 ` Jerome Brunet
2017-08-02 10:07 ` Shawn Lin
2017-08-02 10:07 ` Shawn Lin
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