On 30/10/2020 16:58, Maxime Ripard wrote:
> Hi!
>
> I was playing around with some code to generate EDIDs, and I think I
> found a bug in how edid-decode parses the landscape and portrait ratio
> in the base block, bytes 0x15 and 0x16.
>
> The spec (section 3.6.2) provides a formula to get back the aspect ratio
> from the stored value which is:
>
> in landscape
> aspect ratio = (stored value + 99) / 100
>
> With the value in the byte 0x15
>
> and in portrait
> aspect ratio = 100 / (stored value + 99)
>
> with the value in the byte 0x16
>
> However, parse-base-block.cpp has:
>
> if (x[0x15])
> printf(" Aspect ratio: %f (landscape)\n", 100.0 / (x[0x16] + 99));
> else
> printf(" Aspect ratio: %f (portrait)\n", 100.0 / (x[0x15] + 99));
>
> Which applies the same formula to both ratio types, and seems to invert
> the bytes supposed to be used?
>
> The spec provides some example later on, for example with 4/3 (so
> 1.333333...) where the stored value is supposed to be 34/0x22, while
> edid-decode parses that as 1.010101
Yup, it's wrong. It's a very old bug, it was already there before I became
maintainer of edid-decode. So not my fault :-)
Thanks!
Hans
