Hi Jani,
I can now see /dev/drm_dp_aux*.
I'm not familiar with dd command.Correct me if I'm wrong.
Possible commands i tried and nothing happen:dd if=/dev/drm_dp_aux1 seek=723
ibs=2dd of=/dev/drm_dp_aux1 seek=723 ibs=2
dd if=/dev/drm_dp_aux2 seek=723 ibs=2dd of=/dev/drm_dp_aux2 seek=723 ibs=2
I assumed I could read the brightness msb and lsb using the define in
drm_dp_helper.h.
#define DP_EDP_BACKLIGHT_BRIGHTNESS_MSB 0x722#define
DP_EDP_BACKLIGHT_BRIGHTNESS_LSB 0x723
>From here, I was thinking if I could try to open \dev\drm_dp_aux* then read
>the brightness offset 0x723, though not sure how to proceed with it.I was able
>to successfully open \dev\drm_dp_aux1 and \dev\drm_dp_aux2 but I thinking I'm
>wrong when I proceed to ioctl because they all failed.
#define BRIGHTNESS 0x723
int main(int argc, char ** argv){ int fd; int retcode; char out[128];
if((fd = open("/dev/drm_dp_aux1",O_RDWR)) >=0) { printf("open success"); }
else { printf("open failed");
}
if((retcode = ioctl(fd,BRIGHTNESS,&out)) < 0) { printf("ioctl failed");
} else { printf("ioctl success");
}
// trying aux2 if((fd = open("/dev/drm_dp_aux2",O_RDWR)) >=0) {
printf("open success"); } else { printf("open failed");
}
if((retcode = ioctl(fd,BRIGHTNESS,&out)) < 0) { printf("ioctl failed");
} else { printf("ioctl success");
}
return 0;}
Thanks,John
On Thursday, May 24, 2018, 8:38:02 PM GMT+8, Jani Nikula
<[email protected]> wrote:
On Thu, 24 May 2018, John Sledge <[email protected]> wrote:
> I was able to update my kernel to 4.6 which has the DRM_DP_AUX_CHARDEV
> in the Kconfig file linux-4.6\drivers\gpu\drm. Though I also
> add DRM_DP_AUX_CHARDEV=y in kernel config. When invoke uname -r, I
> could see that the kernel is now 4.6.
If you're updating kernels, why not update to a recent kernel that's
actually supported...?
> How can I verify the DRM_DP_AUX_CHARDEV takes effect or got configure
> it correctly?
Boot the kernel, run 'ls /dev/drm_dp_aux*'. If you see stuff, you got it
right.
> It still unclear to me how to follow what you mean by using DRM DP AUX
> interface and getting /dev/drm_dp_auxN node(s) that allows me to read
> and write arbitrary DPCD offsets.
The device is a char device you can open, seek to an offset (which would
be the DPCD offset), and read. For testing, you can achieve the same
using dd.
BR,
Jani.
--
Jani Nikula, Intel Open Source Graphics Center
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