On Fri, 06 Feb 2026, Samasth Norway Ananda <[email protected]>
wrote:
> When reading exactly 512 bytes with burst read enabled, the
> extra_byte_added path breaks out of the inner do-while without
> decrementing len. The outer while(len) then re-enters and gmbus_wait()
> times out since all data has been delivered. Decrement len before the
> break so the outer loop terminates correctly.
Nice find, and the fix looks correct. How did you figure this out? Did
you hit the issue?
I wonder if the whole extra byte thing is a workaround for some old
hardware that shouldn't be needed on modern hardware... Ville, thoughts?
> Also fix a typo in a nearby comment ("generata" -> "generate").
"Also" is a good hint that it should be a separate patch. ;)
BR,
Jani
> Fixes: d5dc0f43f268 ("drm/i915/gmbus: Enable burst read")
> Signed-off-by: Samasth Norway Ananda <[email protected]>
> ---
> drivers/gpu/drm/i915/display/intel_gmbus.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_gmbus.c
> b/drivers/gpu/drm/i915/display/intel_gmbus.c
> index 2caff677600c..5fb3fee34af4 100644
> --- a/drivers/gpu/drm/i915/display/intel_gmbus.c
> +++ b/drivers/gpu/drm/i915/display/intel_gmbus.c
> @@ -496,8 +496,10 @@ gmbus_xfer_read_chunk(struct intel_display *display,
>
> val = intel_de_read_fw(display, GMBUS3(display));
> do {
> - if (extra_byte_added && len == 1)
> + if (extra_byte_added && len == 1) {
> + len--;
> break;
> + }
>
> *buf++ = val & 0xff;
> val >>= 8;
> @@ -693,7 +695,7 @@ do_gmbus_xfer(struct i2c_adapter *adapter, struct i2c_msg
> *msgs, int num,
> goto clear_err;
> }
>
> - /* Generate a STOP condition on the bus. Note that gmbus can't generata
> + /* Generate a STOP condition on the bus. Note that gmbus can't generate
> * a STOP on the very first cycle. To simplify the code we
> * unconditionally generate the STOP condition with an additional gmbus
> * cycle. */
--
Jani Nikula, Intel
