linux-kernel - [PATCH 1/2 v2] gpio/gpio-generic: read correct set register for caching if available

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Date:	Wed, 20 Jul 2011 09:24:32 +0200
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Grant Likely <grant.likely@...retlab.ca>
Cc:	linux-kernel@...r.kernel.org, sodaville@...utronix.de
Subject: [PATCH 1/2 v2] gpio/gpio-generic: read correct set register for
 caching if available

The ->data is a shadow copy which is used during the ->set callback in
order to avoid a read of the register before write.
If ->reg_set is set then we write to this location therefore we should
cache that value.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
* Grant Likely | 2011-07-04 09:44:47 [-0600]:

>On most of the gpio controllers that I've seen, the 'set' register
>isn't something that you can actually read.  I don't think this is
>something that can be done for all gpio controllers.

I have reworked the part to only read the set register only if not
set/clear mode. Is this okay or are they any controller where this does
not work?

 drivers/gpio/gpio-generic.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/drivers/gpio/gpio-generic.c b/drivers/gpio/gpio-generic.c
index 231714d..5234b20 100644
--- a/drivers/gpio/gpio-generic.c
+++ b/drivers/gpio/gpio-generic.c
@@ -398,7 +398,10 @@ int __devinit bgpio_init(struct bgpio_chip *bgc,
 	if (ret)
 		return ret;
 
-	bgc->data = bgc->read_reg(bgc->reg_dat);
+	if (bgc->reg_set == bgpio_set_set)
+		bgc->data = bgc->read_reg(bgc->reg_set);
+	else if (bgc->reg_set == bgpio_set)
+		bgc->data = bgc->read_reg(bgc->reg_dat);
 
 	return ret;
 }
-- 
1.7.4.4

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