linux-kernel - [PATCH 4.4 005/101] pwm: fsl-ftm: Use flat regmap cache

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Date:   Fri, 19 Jun 2020 16:31:54 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Stefan Agner <stefan@...er.ch>,
        Mark Brown <broonie@...nel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Krzysztof Kozlowski <krzk@...nel.org>
Subject: [PATCH 4.4 005/101] pwm: fsl-ftm: Use flat regmap cache

From: Stefan Agner <stefan@...er.ch>

commit ad06fdeeef1cbadf86ebbe510e8079abada8b44e upstream.

Use flat regmap cache to avoid lockdep warning at probe:

[    0.697285] WARNING: CPU: 0 PID: 1 at kernel/locking/lockdep.c:2755 lockdep_trace_alloc+0x15c/0x160()
[    0.697449] DEBUG_LOCKS_WARN_ON(irqs_disabled_flags(flags))

The RB-tree regmap cache needs to allocate new space on first writes.
However, allocations in an atomic context (e.g. when a spinlock is held)
are not allowed. The function regmap_write calls map->lock, which
acquires a spinlock in the fast_io case. Since the pwm-fsl-ftm driver
uses MMIO, the regmap bus of type regmap_mmio is being used which has
fast_io set to true.

The MMIO space of the pwm-fsl-ftm driver is reasonable condense, hence
using the much faster flat regmap cache is anyway the better choice.

Signed-off-by: Stefan Agner <stefan@...er.ch>
Cc: Mark Brown <broonie@...nel.org>
Signed-off-by: Thierry Reding <thierry.reding@...il.com>
Signed-off-by: Krzysztof Kozlowski <krzk@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/pwm/pwm-fsl-ftm.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/pwm/pwm-fsl-ftm.c
+++ b/drivers/pwm/pwm-fsl-ftm.c
@@ -392,7 +392,7 @@ static const struct regmap_config fsl_pw

 	.max_register = FTM_PWMLOAD,
 	.volatile_reg = fsl_pwm_volatile_reg,
-	.cache_type = REGCACHE_RBTREE,
+	.cache_type = REGCACHE_FLAT,
 };

 static int fsl_pwm_probe(struct platform_device *pdev)