[patch] gpiolib: fix oops in gpio_get_value_cansleep()

From: David Brownell
Date: Thu Oct 16 2008 - 11:45:49 EST

From: David Brownell <dbrownell@xxxxxxxxxxxxxxxxxxxxx>

We can get the following oops from gpio_get_value_cansleep()
when a GPIO controller doesn't provide a get() callback:

Unable to handle kernel paging request for instruction fetch
Faulting instruction address: 0x00000000
Oops: Kernel access of bad area, sig: 11 [#1]
NIP [00000000] 0x0
LR [c0182fb0] gpio_get_value_cansleep+0x40/0x50
Call Trace:
[c7b79e80] [c0183f28] gpio_value_show+0x5c/0x94
[c7b79ea0] [c01a584c] dev_attr_show+0x30/0x7c
[c7b79eb0] [c00d6b48] fill_read_buffer+0x68/0xe0
[c7b79ed0] [c00d6c54] sysfs_read_file+0x94/0xbc
[c7b79ef0] [c008f24c] vfs_read+0xb4/0x16c
[c7b79f10] [c008f580] sys_read+0x4c/0x90
[c7b79f40] [c0013a14] ret_from_syscall+0x0/0x38

It's OK to request the value of *any* GPIO; most GPIOs are
bidirectional, so configuring them as outputs just enables an
output driver and doesn't disable the input logic.

So the problem is that gpio_get_value_cansleep() isn't making
the same sanity check that gpio_get_value() does: making sure
this GPIO isn't one of the atypical "no input logic" cases.

Reported-by: Anton Vorontsov <avorontsov@xxxxxxxxxxxxx>
Signed-off-by: David Brownell <dbrownell@xxxxxxxxxxxxxxxxxxxxx>
drivers/gpio/gpiolib.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -1056,7 +1056,7 @@ int gpio_get_value_cansleep(unsigned gpi

chip = gpio_to_chip(gpio);
- return chip->get(chip, gpio - chip->base);
+ return chip->get ? chip->get(chip, gpio - chip->base) : 0;

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