spi: spi-qpic-snand: document the limited bit error reporting capability

The QPIC hardware is not capable of reporting the exact number of the
corrected bit errors, it only reports the number of the corrected bytes.

Document this behaviour in the code, and also issue a warning message
to inform the user about it.

No functional changes.

Signed-off-by: Gabor Juhos <j4g8y7@gmail.com>
Link: https://patch.msgid.link/20250527-qpic-snand-limited-biterr-caps-v1-1-61f7cf87be1e@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: juhosg

drivers/spi/spi-qpic-snand.c

@@ -639,6 +639,20 @@ static int qcom_spi_check_error(struct qcom_nand_controller *snandc)
 			unsigned int stat;
 
 			stat = buffer & BS_CORRECTABLE_ERR_MSK;
+
+			/*
+			 * The exact number of the corrected bits is
+			 * unknown because the hardware only reports the
+			 * number of the corrected bytes.
+			 *
+			 * Since we have no better solution at the moment,
+			 * report that value as the number of bit errors
+			 * despite that it is inaccurate in most cases.
+			 */
+			if (stat && stat != ecc_cfg->strength)
+				dev_warn_once(snandc->dev,
+					      "Warning: due to hw limitation, the reported number of the corrected bits may be inaccurate\n");
+
 			snandc->qspi->ecc_stats.corrected += stat;
 			max_bitflips = max(max_bitflips, stat);
 		}