[PATCH 1/2 v2] gpio/gpio-generic: read correct set register forcaching if available

From: Sebastian Andrzej Siewior
Date: Wed Jul 20 2011 - 03:24:39 EST

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@xxxxxxxxxxxxx>
* 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;

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