On 2/10/26 1:23 AM, Jani Nikula wrote:
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 came across it while working on a different issue and was reading the
code.
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. ;)
Thanks. I will send out a v2 with separate patches :)
Samasth.
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. */
