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Commit 4819d2e4 authored by Chris Wilson's avatar Chris Wilson Committed by Dave Airlie
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drm: Retry i2c transfer of EDID block after failure 



Usually EDID retrieval is fine. However, sometimes, especially when the
machine is loaded, it fails, but succeeds after a few retries.

Based on a patch by Michael Buesch.

Reported-by: default avatarMichael Buesch <mb@bu3sch.de>
Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: default avatarAlex Deucher <alexdeucher@gmail.com>
Signed-off-by: default avatarDave Airlie <airlied@redhat.com>
parent 942b0e95

drivers/gpu/drm/drm_edid.c

+24 −16
Original line number Diff line number Diff line
@@ -230,6 +230,15 @@ drm_do_probe_ddc_edid(struct i2c_adapter *adapter, unsigned char *buf, 
		      int block, int len)

{

	unsigned char start = block * EDID_LENGTH;

	int ret, retries = 5;



	/* The core i2c driver will automatically retry the transfer if the

	 * adapter reports EAGAIN. However, we find that bit-banging transfers

	 * are susceptible to errors under a heavily loaded machine and

	 * generate spurious NAKs and timeouts. Retrying the transfer

	 * of the individual block a few times seems to overcome this.

	 */

	do {

		struct i2c_msg msgs[] = {

			{

				.addr	= DDC_ADDR,
@@ -243,11 +252,10 @@ drm_do_probe_ddc_edid(struct i2c_adapter *adapter, unsigned char *buf, 
				.buf	= buf,

			}

		};

		ret = i2c_transfer(adapter, msgs, 2);

	} while (ret != 2 && --retries);



	if (i2c_transfer(adapter, msgs, 2) == 2)

		return 0;



	return -1;

	return ret == 2 ? 0 : -1;

}



static u8 *