[PATCH] drm/amdgpu: use ACK polling for page-write completion

[Kunal Zodape]

The EEPROM write path currently waits a fixed 10 ms after each page
write to cover the maximum write-cycle time.

Replace the fixed delay with ACK polling so the driver can continue as
soon as the EEPROM finishes its internal write cycle. Since the SMU I2C
adapter used for these EEPROM accesses does not support zero-length
transfers, poll readiness with an offset-only dummy write.

Keep the existing 10 ms timeout as the upper bound for the polling loop.

Tested on MI200 (ALDEBARAN) with ras_eeprom_reset confirming clean
write/read-back with no I2C errors.

Signed-off-by: Kunal Zodape <kunal.devanandzodape@xxxxxxx>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_eeprom.c | 28 +++++++++++++++-------
 1 file changed, 20 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_eeprom.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_eeprom.c
index 8cd69836dd99..53be5a31c40c 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_eeprom.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_eeprom.c
@@ -153,15 +153,27 @@ static int __amdgpu_eeprom_xfer(struct i2c_adapter *i2c_adap, u32 eeprom_addr,
 			break;
 
 		if (!read) {
-			/* According to EEPROM specs the length of the
-			 * self-writing cycle, tWR (tW), is 10 ms.
-			 *
-			 * TODO: Use polling on ACK, aka Acknowledge
-			 * Polling, to minimize waiting for the
-			 * internal write cycle to complete, as it is
-			 * usually smaller than tWR (tW).
+			ktime_t timeout = ktime_add_ms(ktime_get(), 10);
+
+			/* Poll for ACK to detect when the self-timed
+			 * internal write cycle has completed, as per
+			 * Acknowledge Polling described in the AT24CM02
+			 * datasheet, Section 7.4. The SMU I2C adapter
+			 * used by these EEPROM paths does not support
+			 * zero-length messages, so use an offset-only
+			 * dummy write to probe for the ACK. The address
+			 * pointer update is harmless because each real
+			 * transfer reprograms it before use.
 			 */
-			msleep(10);
+			do {
+				r = i2c_transfer(i2c_adap, &msgs[0], 1);
+				if (r == 1)
+					break;
+				usleep_range(100, 200);
+			} while (ktime_before(ktime_get(), timeout));
+
+			if (r != 1)
+				break;
 		}
 	}
 
-- 
2.17.1