linux-kernel - [PATCH 5.4 428/434] mmc: sdhci-of-esdhc: Revert "mmc: sdhci-of-esdhc: add erratum A-009204 support"

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Date:   Sun, 29 Dec 2019 18:28:01 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Ulf Hansson <ulf.hansson@...aro.org>
Subject: [PATCH 5.4 428/434] mmc: sdhci-of-esdhc: Revert "mmc: sdhci-of-esdhc: add erratum A-009204 support"

From: Rasmus Villemoes <linux@...musvillemoes.dk>

commit 8b6dc6b2d60221e90703babbc141f063b8a07e72 upstream.

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>
Cc: stable@...r.kernel.org
Link: https://lore.kernel.org/r/20191204085447.27491-1-linux@rasmusvillemoes.dk
Signed-off-by: Ulf Hansson <ulf.hansson@...aro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

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

--- a/drivers/mmc/host/sdhci-of-esdhc.c
+++ b/drivers/mmc/host/sdhci-of-esdhc.c
@@ -710,9 +710,6 @@ static void esdhc_reset(struct sdhci_hos
 	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;