On Tue, Dec 31, 2019 at 03:30:47AM +0000, Lin, Wayne wrote:
[AMD Official Use Only - Internal Distribution Only]
From: Jani Nikula jani.nikula@linux.intel.com Sent: Monday, December 30, 2019 19:15 To: Lin, Wayne; dri-devel@lists.freedesktop.org; amd-gfx@lists.freedesktop.org Cc: Zuo, Jerry; Kazlauskas, Nicholas; Lin, Wayne Subject: Re: [PATCH] drm/dp_mst: correct the shifting in DP_REMOTE_I2C_READ
On Mon, 30 Dec 2019, Wayne Lin Wayne.Lin@amd.com wrote:
[Why] According to DP spec, it should shift left 4 digits for NO_STOP_BIT in REMOTE_I2C_READ message. Not 5 digits.
[How] Correct the shifting value of NO_STOP_BIT for DP_REMOTE_I2C_READ case in drm_dp_encode_sideband_req().
Which commit introduced the issue? Fixes: tag. Does it need a stable backport? Does this fix a user visible bug?
BR, Jani.
Thanks for your time and reminder.
It seems like the issue has been there since very beginning.(commit: ad7f8a1). It doesn't introduce user visible bug under my test cases, but this affects the I2C signal between I2C master and I2C slave. Not pretty sure if there is any eeprom will reset the written offset once received I2C stop. If so, that might cause wrongly reading EDID. I will Cc to stable. Thanks.
The segment address should be reset on STOP. So large EDIDs should fail. IIRC we had a bug report of some sort about this which I tried to fix by confgiuring .no_stop_bit correctly, but apparently I failed to double check that the bit get stuffed onto the wire correctly.
Ah yes, https://bugs.freedesktop.org/show_bug.cgi?id=108081 So you may have just fixed that one, although we seem to have closed it already.
Signed-off-by: Wayne Lin Wayne.Lin@amd.com
drivers/gpu/drm/drm_dp_mst_topology.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c index 1d1bfa49ca2b..0557e225ff67 100644 --- a/drivers/gpu/drm/drm_dp_mst_topology.c +++ b/drivers/gpu/drm/drm_dp_mst_topology.c @@ -393,7 +393,7 @@ drm_dp_encode_sideband_req(const struct drm_dp_sideband_msg_req_body *req, memcpy(&buf[idx], req->u.i2c_read.transactions[i].bytes, req->u.i2c_read.transactions[i].num_bytes); idx += req->u.i2c_read.transactions[i].num_bytes;
buf[idx] = (req->u.i2c_read.transactions[i].no_stop_bit & 0x1) << 5;
buf[idx] = (req->u.i2c_read.transactions[i].no_stop_bit & 0x1) << 4; buf[idx] |= (req->u.i2c_read.transactions[i].i2c_transaction_delay & 0xf); idx++; }-- Jani Nikula, Intel Open Source Graphics Center
-- Wayne Lin _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel