On Fri, Jan 26, 2024 at 7:55 PM Mario Limonciello <mario.limonciello@xxxxxxx> wrote: > > The ACPI specification allows for an EDID to be up to 512 bytes but > the _DDC EDID fetching code will only try up to 256 bytes. > > Modify the code to instead start at 512 bytes and work it's way > down instead. > > Link: https://uefi.org/htmlspecs/ACPI_Spec_6_4_html/Apx_B_Video_Extensions/output-device-specific-methods.html#ddc-return-the-edid-for-this-device > Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxx> > --- > drivers/acpi/acpi_video.c | 23 ++++++++++++++++------- > 1 file changed, 16 insertions(+), 7 deletions(-) > > diff --git a/drivers/acpi/acpi_video.c b/drivers/acpi/acpi_video.c > index 62f4364e4460..b3b15dd4755d 100644 > --- a/drivers/acpi/acpi_video.c > +++ b/drivers/acpi/acpi_video.c > @@ -624,6 +624,10 @@ acpi_video_device_EDID(struct acpi_video_device *device, > arg0.integer.value = 1; > else if (length == 256) > arg0.integer.value = 2; > + else if (length == 384) > + arg0.integer.value = 3; > + else if (length == 512) > + arg0.integer.value = 4; It looks like switch () would be somewhat better. Or maybe even arg0.integer.value = length / 128; The validation could be added too: if (arg0.integer.value > 4 || arg0.integer.value * 128 != length) return -EINVAL; but it is pointless, because the caller is never passing an invalid number to it AFAICS. > else > return -EINVAL; > > @@ -1443,7 +1447,7 @@ int acpi_video_get_edid(struct acpi_device *device, int type, int device_id, > > for (i = 0; i < video->attached_count; i++) { > video_device = video->attached_array[i].bind_info; > - length = 256; > + length = 512; > > if (!video_device) > continue; > @@ -1478,13 +1482,18 @@ int acpi_video_get_edid(struct acpi_device *device, int type, int device_id, > > if (ACPI_FAILURE(status) || !buffer || > buffer->type != ACPI_TYPE_BUFFER) { > - length = 128; > - status = acpi_video_device_EDID(video_device, &buffer, > - length); > - if (ACPI_FAILURE(status) || !buffer || > - buffer->type != ACPI_TYPE_BUFFER) { > - continue; > + while (length) { I would prefer a do {} while () loop here, which could include the first invocation of acpi_video_device_EDID() too (and reduce code duplication a bit). > + length -= 128; > + status = acpi_video_device_EDID(video_device, &buffer, > + length); No line break, please. > + if (ACPI_FAILURE(status) || !buffer || > + buffer->type != ACPI_TYPE_BUFFER) { > + continue; > + } > + break; > } > + if (!length) > + continue; > } > > *edid = buffer->buffer.pointer; > --
