linux-kernel - [PATCH] gpio: pca953x: Don't flip bits on PCA957x GPIO expanders when probing them.

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Message-Id: <1375478656-3577-1-git-send-email-gsmecher@threespeedlogic.com>
Date:	Fri,  2 Aug 2013 14:24:16 -0700
From:	Graeme Smecher <gsmecher@...eespeedlogic.com>
To:	linux-kernel@...r.kernel.org
Cc:	Graeme Smecher <gsmecher@...eespeedlogic.com>,
	Grant Likely <grant.likely@...aro.org>,
	Haojian Zhuang <haojian.zhuang@...vell.com>
Subject: [PATCH] gpio: pca953x: Don't flip bits on PCA957x GPIO expanders when probing them.

The pca957x driver supports a handful of I2C GPIO expanders from NXP, Maxim,
and TI. For the PCA9574 and PCA9575 devices only, the driver resets the GPIO
level and direction in the pca957x_probe function. This seems like the wrong
thing to do, since it can cause hardware bit twiddles during warm reboots when
the chip state and reset values don't match.

This kind of initialization is best left upstream (in a bootloader) or
downstream (in userspace). It's also an inconsistency across devices supported
by this driver.

Signed-off-by: Graeme Smecher <gsmecher@...eespeedlogic.com>
Cc: Grant Likely <grant.likely@...aro.org>
Cc: Haojian Zhuang <haojian.zhuang@...vell.com>
---
 drivers/gpio/gpio-pca953x.c |   11 -----------
 1 file changed, 11 deletions(-)

diff --git a/drivers/gpio/gpio-pca953x.c b/drivers/gpio/gpio-pca953x.c
index 426c51d..47c08d8 100644
--- a/drivers/gpio/gpio-pca953x.c
+++ b/drivers/gpio/gpio-pca953x.c
@@ -683,17 +683,6 @@ static int device_pca957x_init(struct pca953x_chip *chip, u32 invert)
 	int ret;
 	u8 val[MAX_BANK];
 
-	/* Let every port in proper state, that could save power */
-	memset(val, 0, NBANK(chip));
-	pca953x_write_regs(chip, PCA957X_PUPD, val);
-	memset(val, 0xFF, NBANK(chip));
-	pca953x_write_regs(chip, PCA957X_CFG, val);
-	memset(val, 0, NBANK(chip));
-	pca953x_write_regs(chip, PCA957X_OUT, val);
-
-	ret = pca953x_read_regs(chip, PCA957X_IN, val);
-	if (ret)
-		goto out;
 	ret = pca953x_read_regs(chip, PCA957X_OUT, chip->reg_output);
 	if (ret)
 		goto out;
-- 
1.7.10.4

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