linux-kernel - [PATCH] mmd: core: Terminate infinite loop in SD-UHS voltage switch

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Date:   Tue, 13 Sep 2022 18:40:10 -0700
From:   Brian Norris <briannorris@...omium.org>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Guenter Roeck <linux@...ck-us.net>,
        Brian Norris <briannorris@...omium.org>,
        stable@...r.kernel.org, Arindam Nath <arindam.nath@....com>,
        Chris Ball <cjb@...top.org>,
        Philip Rakity <prakity@...vell.com>,
        Zhangfei Gao <zhangfei.gao@...vell.com>,
        linux-kernel@...r.kernel.org, linux-mmc@...r.kernel.org
Subject: [PATCH] mmd: core: Terminate infinite loop in SD-UHS voltage switch

This loop intends to retry a max of 10 times, with some implicit
termination based on the SD_{R,}OCR_S18A bit. Unfortunately, the
termination condition depends on the value reported by the SD card
(*rocr), which may or may not correctly reflect what we asked it to do.

Needless to say, it's not wise to rely on the card doing what we expect;
we should at least terminate the loop regardless. So, check both the
input and output values, so we ensure we will terminate regardless of
the SD card behavior.

Note that SDIO learned a similar retry loop in commit 0797e5f1453b
("mmc: core: Fixup signal voltage switch"), but that used the 'ocr'
result, and so the current pre-terminating condition looks like:

    rocr & ocr & R4_18V_PRESENT

(i.e., it doesn't have the same bug.)

This addresses a number of crash reports seen on ChromeOS that look
like the following:

    ... // lots of repeated: ...
    <4>[13142.846061] mmc1: Skipping voltage switch
    <4>[13143.406087] mmc1: Skipping voltage switch
    <4>[13143.964724] mmc1: Skipping voltage switch
    <4>[13144.526089] mmc1: Skipping voltage switch
    <4>[13145.086088] mmc1: Skipping voltage switch
    <4>[13145.645941] mmc1: Skipping voltage switch
    <3>[13146.153969] INFO: task halt:30352 blocked for more than 122 seconds.
    ...

Fixes: f2119df6b764 mmc: sd: add support for signal voltage switch procedure
Cc: <stable@...r.kernel.org>
Signed-off-by: Brian Norris <briannorris@...omium.org>
---

 drivers/mmc/core/sd.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/mmc/core/sd.c b/drivers/mmc/core/sd.c
index 06aa62ce0ed1..3662bf5320ce 100644
--- a/drivers/mmc/core/sd.c
+++ b/drivers/mmc/core/sd.c
@@ -870,7 +870,8 @@ int mmc_sd_get_cid(struct mmc_host *host, u32 ocr, u32 *cid, u32 *rocr)
 	 * the CCS bit is set as well. We deliberately deviate from the spec in
 	 * regards to this, which allows UHS-I to be supported for SDSC cards.
 	 */
-	if (!mmc_host_is_spi(host) && rocr && (*rocr & SD_ROCR_S18A)) {
+	if (!mmc_host_is_spi(host) && (ocr & SD_OCR_S18R) &&
+	    rocr && (*rocr & SD_ROCR_S18A)) {
 		err = mmc_set_uhs_voltage(host, pocr);
 		if (err == -EAGAIN) {
 			retries--;
-- 
2.37.2.789.g6183377224-goog