mtd: rawnand: Introduce nand_choose_best_sdr_timings()

Extract the logic out of nand_choose_interface_config() to create a
public helper that can be reused by manufacturer drivers. Add the
possibility to provide a specific set of timings.
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://lore.kernel.org/linux-mtd/20200529111322.7184-22-miquel.raynal@bootlin.com

drivers/mtd/nand/raw/internals.h

@@ -90,6 +90,9 @@ void onfi_fill_interface_config(struct nand_chip *chip,
 				unsigned int timing_mode);
 unsigned int
 onfi_find_closest_sdr_mode(const struct nand_sdr_timings *spec_timings);
+int nand_choose_best_sdr_timings(struct nand_chip *chip,
+				 struct nand_interface_config *iface,
+				 struct nand_sdr_timings *spec_timings);
 int nand_get_features(struct nand_chip *chip, int addr, u8 *subfeature_param);
 int nand_set_features(struct nand_chip *chip, int addr, u8 *subfeature_param);
 int nand_read_page_raw_notsupp(struct nand_chip *chip, u8 *buf,

drivers/mtd/nand/raw/nand_base.c

@@ -1005,6 +1005,62 @@ static int nand_setup_interface(struct nand_chip *chip, int chipnr)
 	return ret;
 }
 
+/**
+ * nand_choose_best_sdr_timings - Pick up the best SDR timings that both the
+ *                                NAND controller and the NAND chip support
+ * @chip: the NAND chip
+ * @iface: the interface configuration (can eventually be updated)
+ * @spec_timings: specific timings, when not fitting the ONFI specification
+ *
+ * If specific timings are provided, use them. Otherwise, try to retrieve
+ * supported timing modes from ONFI information. Finally, if the NAND chip does
+ * not follow the ONFI specification, rely on the ->default_timing_mode
+ * specified in the nand_ids table.
+ */
+int nand_choose_best_sdr_timings(struct nand_chip *chip,
+				 struct nand_interface_config *iface,
+				 struct nand_sdr_timings *spec_timings)
+{
+	const struct nand_controller_ops *ops = chip->controller->ops;
+	int best_mode = 0, mode, ret;
+
+	iface->type = NAND_SDR_IFACE;
+
+	if (spec_timings) {
+		iface->timings.sdr = *spec_timings;
+		iface->timings.mode = onfi_find_closest_sdr_mode(spec_timings);
+
+		/* Verify the controller supports the requested interface */
+		ret = ops->setup_interface(chip, NAND_DATA_IFACE_CHECK_ONLY,
+					   iface);
+		if (!ret)
+			return ret;
+
+		/* Fallback to slower modes */
+		best_mode = iface->timings.mode;
+	} else {
+		if (chip->parameters.onfi) {
+			unsigned int onfi_modes;
+
+			onfi_modes = chip->parameters.onfi->async_timing_mode;
+			best_mode = fls(onfi_modes) - 1;
+		} else {
+			best_mode = chip->onfi_timing_mode_default;
+		}
+	}
+
+	for (mode = best_mode; mode >= 0; mode--) {
+		onfi_fill_interface_config(chip, iface, NAND_SDR_IFACE, mode);
+
+		ret = ops->setup_interface(chip, NAND_DATA_IFACE_CHECK_ONLY,
+					   iface);
+		if (!ret)
+			return 0;
+	}
+
+	return 0;
+}
+
 /**
  * nand_choose_interface_config - find the best data interface and timings
  * @chip: The NAND chip
@@ -1016,48 +1072,14 @@ static int nand_setup_interface(struct nand_chip *chip, int chipnr)
  * ->onfi_timing_mode_default specified in the nand_ids table. After this
  * function nand_chip->interface_ is initialized with the best timing mode
  * available.
- *
- * Returns 0 for success or negative error code otherwise.
  */
 static int nand_choose_interface_config(struct nand_chip *chip)
 {
-	int modes, mode, ret;
-
 	if (!nand_controller_can_setup_interface(chip))
 		return 0;
 
-	/*
-	 * First try to identify the best timings from ONFI parameters and
-	 * if the NAND does not support ONFI, fallback to the default ONFI
-	 * timing mode.
-	 */
-	if (chip->parameters.onfi) {
-		modes = chip->parameters.onfi->async_timing_mode;
-	} else {
-		if (!chip->onfi_timing_mode_default)
-			return 0;
-
-		modes = GENMASK(chip->onfi_timing_mode_default, 0);
-	}
-
-	for (mode = fls(modes) - 1; mode >= 0; mode--) {
-		onfi_fill_interface_config(chip, &chip->interface_config,
-					   NAND_SDR_IFACE, mode);
-
-		/*
-		 * Pass NAND_DATA_IFACE_CHECK_ONLY to only check if the
-		 * controller supports the requested timings.
-		 */
-		ret = chip->controller->ops->setup_interface(chip,
-						 NAND_DATA_IFACE_CHECK_ONLY,
-						 &chip->interface_config);
-		if (!ret) {
-			chip->onfi_timing_mode_default = mode;
-			break;
-		}
-	}
-
-	return 0;
+	return nand_choose_best_sdr_timings(chip, &chip->interface_config,
+					    NULL);
 }
 
 /**