Messages in this thread |  | | | Date | Fri, 26 Feb 2010 11:47:35 -0600 | | Subject | Re: [PATCH] OLPC: ALSA: fix cs5535audio's MIC GPIO to enable input | | From | Ben Gardner <> |
| |
Hi Andres,
> Previously the MIC GPIO was set to output mode, and when checking the status > after setting it we were checking OUTPUT_VAL. This worked, though I'm not > quite sure why. Instead, if we actually check the READ_BACK value, it > doesn't work unless the GPIO is in bidirectional mode. Thus, enable > input mode as well.
The cs5535-gpio driver was reading output value, not the sensed input value. When that was fixed, this OLPC code failed because the input wasn't enabled, so the gpio_get_value() call didn't return anything useful. At reset the CS5535/6 GPIOs have both input and output disabled.
> Signed-off-by: Andres Salomon <dilinger@collabora.co.uk> > --- > sound/pci/cs5535audio/cs5535audio_olpc.c | 1 + > 1 files changed, 1 insertions(+), 0 deletions(-) > > diff --git a/sound/pci/cs5535audio/cs5535audio_olpc.c b/sound/pci/cs5535audio/cs5535audio_olpc.c > index 50da49b..f5574f2 100644 > --- a/sound/pci/cs5535audio/cs5535audio_olpc.c > +++ b/sound/pci/cs5535audio/cs5535audio_olpc.c > @@ -157,6 +157,7 @@ int __devinit olpc_quirks(struct snd_card *card, struct snd_ac97 *ac97) > return -EIO; > } > gpio_direction_output(OLPC_GPIO_MIC_AC, 0); > + gpio_direction_input(OLPC_GPIO_MIC_AC); > > /* drop the original AD1888 HPF control */ > memset(&elem, 0, sizeof(elem));
This will only work because the cs5535-gpio driver and gpiolib are both 'broken'.
The problem with gpiolib is that it only allows a GPIO pin to be either an input or output, but not both. It has two separate functions to configure the direction (gpio_direction_input/gpio_direction_output), where one should do (ie, gpio_set_direction). From what I can tell, when direction_input() is called, the GPIO chip is expected to disable the output and enable the input. If that really occurred, then the above code would still be broken.
The cs5535-gpio driver doesn't follow that input-or-output convention. It never disables the direction that wasn't requested.
I'm working on a gpiolib patch that will combine gpio_direction_output and gpio_direction_input into one function. That would enable the above driver to be 'obviously correct'.
Ben -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
|  |