linux-kernel - [PATCH v3] mmc: Make ID freq configurable

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Date:	Sun, 3 Jan 2010 09:23:30 +1100
From:	Ben Nizette <bn@...sdigital.com>
To:	Pierre Ossman <pierre@...man.eu>
Cc:	Hein_Tibosch <hein_tibosch@...oo.es>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Adrian Hunter <adrian.hunter@...ia.com>,
	linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
	Matt Fleming <matt@...sole-pimps.org>
Subject: [PATCH v3] mmc: Make ID freq configurable


On 02/01/2010, at 11:08 PM, Pierre Ossman wrote:

> On Sat, 2 Jan 2010 20:07:01 +1100
> Ben Nizette <bn@...sdigital.com> wrote:
> 
>> 
>> Pierre, thoughts?  All my cards were borderline spec but Hein's got a mainstream, common card which seems to completely ignore the spec.  Can we just take the few-hundred-uS hit and allow initialization down at the bottom end, say 100kHz?
>> 
> 
> Broken cards seem to be all over the spectrum, so I wouldn't be
> suprised if you find ones that break if you go too low as well.

Yea good point, though given there might not even be a One Freq to Rule Them All, how about:

---8<---

From: Ben Nizette <bn@...sdigital.com>
Subject: [PATCH v3] mmc: Make ID freq configurable

While the SD spec specifies a range of frequencies for the ID phase from 100-400kHz, not all cards play by the rules.  This patch adds a Kconfig option to allow the user to tweak this to their card/host config, though the default of 250kHz should be fine for all spec-abiding cards and most others besides.

Signed-off-by: Ben Nizette <bn@...sdigital.com>

---
diff --git a/drivers/mmc/core/Kconfig b/drivers/mmc/core/Kconfig
index ab37a6d..a8e5003 100644
--- a/drivers/mmc/core/Kconfig
+++ b/drivers/mmc/core/Kconfig
@@ -14,3 +14,15 @@ config MMC_UNSAFE_RESUME
          This option is usually just for embedded systems which use
          a MMC/SD card for rootfs. Most people should say N here.
 
+config MMC_ID_FREQ
+       int "SD/MMC Card initialisation frequency (Hz)"
+       default 250000
+       help
+         The SD card specification allows for initialisation
+         frequencies from 100-400kHz however some broken cards are
+         known not to work across this whole range.
+
+         If you're having problems with a particular card not being
+         detected, you may try adjusting this frequency up or down
+         but for widest compatibility just leave it default.
+
diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index 7dab2e5..2eab68f 100644
--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -891,12 +891,17 @@ static void mmc_power_up(struct mmc_host *host)
         */
        mmc_delay(10);
 
-       if (host->f_min > 400000) {
-               pr_warning("%s: Minimum clock frequency too high for "
-                               "identification mode\n", mmc_hostname(host));
+       /*
+        * CONFIG_MMC_ID_FREQ defaults to 250kHz which should be fine
+        * for most card/host combos.
+        */
+       if (host->f_min > CONFIG_MMC_ID_FREQ) {
+               pr_warning("%s: The host cannot reach the requested ID clock "
+                               "rate, identification may fail\n",
+                               mmc_hostname(host));
                host->ios.clock = host->f_min;
        } else
-               host->ios.clock = 400000;
+               host->ios.clock = CONFIG_MMC_ID_FREQ;
 
        host->ios.power_mode = MMC_POWER_ON;
        mmc_set_ios(host);

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