linux-kernel - [PATCH] mmc: sdhci-of-esdhc: Revert "mmc: sdhci-of-esdhc: add erratum A-009204 support"

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Date:   Wed,  4 Dec 2019 09:54:46 +0100
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Adrian Hunter <adrian.hunter@...el.com>,
        Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Yinbo Zhu <yinbo.zhu@....com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] mmc: sdhci-of-esdhc: Revert "mmc: sdhci-of-esdhc: add erratum A-009204 support"

This reverts commit 5dd195522562542bc6ebe6e7bd47890d8b7ca93c.

First, the fix seems to be plain wrong, since the erratum suggests
waiting 5ms before setting setting SYSCTL[RSTD], but this msleep()
happens after the call of sdhci_reset() which is where that bit gets
set (if SDHCI_RESET_DATA is in mask).

Second, walking the whole device tree to figure out if some node has a
"fsl,p2020-esdhc" compatible string is hugely expensive - about 70 to
100 us on our mpc8309 board. Walking the device tree is done under a
raw_spin_lock, so this is obviously really bad on an -rt system, and a
waste of time on all.

In fact, since esdhc_reset() seems to get called around 100 times per
second, that mpc8309 now spends 0.8% of its time determining that
it is not a p2020. Whether those 100 calls/s are normal or due to some
other bug or misconfiguration, regularly hitting a 100 us
non-preemptible window is unacceptable.

Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
---

The errata sheet for mpc8309 also mentions A-009204, so I'm not at all
opposed to having a fix for that. But it needs to be done properly
without causing a huge performance or latency impact. We should
probably just add a bit to struct sdhci_esdhc which gets initialized
in esdhc_init.

 drivers/mmc/host/sdhci-of-esdhc.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/drivers/mmc/host/sdhci-of-esdhc.c b/drivers/mmc/host/sdhci-of-esdhc.c
index 5cca3fa4610b..7f87a90bf56a 100644
--- a/drivers/mmc/host/sdhci-of-esdhc.c
+++ b/drivers/mmc/host/sdhci-of-esdhc.c
@@ -764,9 +764,6 @@ static void esdhc_reset(struct sdhci_host *host, u8 mask)
 	sdhci_writel(host, host->ier, SDHCI_INT_ENABLE);
 	sdhci_writel(host, host->ier, SDHCI_SIGNAL_ENABLE);

-	if (of_find_compatible_node(NULL, NULL, "fsl,p2020-esdhc"))
-		mdelay(5);
-
 	if (mask & SDHCI_RESET_ALL) {
 		val = sdhci_readl(host, ESDHC_TBCTL);
 		val &= ~ESDHC_TB_EN;
-- 
2.23.0