can: mcp251xfd: ram: add helper function for runtime ring size calculation

This patch adds a helper function to calculate the ring configuration
of the controller based on various constraints, like available RAM,
size of RX and TX objects, CAN-mode, number of FIFOs and FIFO depth.

Link: https://lore.kernel.org/20220313083640.501791-3-mkl@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/spi/mcp251xfd/Makefile

@@ -6,6 +6,7 @@ mcp251xfd-objs :=
 mcp251xfd-objs += mcp251xfd-chip-fifo.o
 mcp251xfd-objs += mcp251xfd-core.o
 mcp251xfd-objs += mcp251xfd-crc16.o
+mcp251xfd-objs += mcp251xfd-ram.o
 mcp251xfd-objs += mcp251xfd-regmap.o
 mcp251xfd-objs += mcp251xfd-ring.o
 mcp251xfd-objs += mcp251xfd-rx.o

drivers/net/can/spi/mcp251xfd/mcp251xfd-ram.c

@@ -0,0 +1,97 @@
+// SPDX-License-Identifier: GPL-2.0
+//
+// mcp251xfd - Microchip MCP251xFD Family CAN controller driver
+//
+// Copyright (c) 2021, 2022 Pengutronix,
+//               Marc Kleine-Budde <kernel@pengutronix.de>
+//
+
+#include "mcp251xfd-ram.h"
+
+static inline u8 can_ram_clamp(const struct can_ram_config *config,
+			       const struct can_ram_obj_config *obj,
+			       u8 val)
+{
+	u8 max;
+
+	max = min_t(u8, obj->max, obj->fifo_num * config->fifo_depth);
+	return clamp(val, obj->min, max);
+}
+
+static u8
+can_ram_rounddown_pow_of_two(const struct can_ram_config *config,
+			     const struct can_ram_obj_config *obj, u8 val)
+{
+	u8 fifo_num = obj->fifo_num;
+	u8 ret = 0, i;
+
+	val = can_ram_clamp(config, obj, val);
+
+	for (i = 0; i < fifo_num && val; i++) {
+		u8 n;
+
+		n = min_t(u8, rounddown_pow_of_two(val),
+			  config->fifo_depth);
+
+		/* skip small FIFOs */
+		if (n < obj->fifo_depth_min)
+			return ret;
+
+		ret += n;
+		val -= n;
+	}
+
+	return ret;
+}
+
+void can_ram_get_layout(struct can_ram_layout *layout,
+			const struct can_ram_config *config,
+			const struct ethtool_ringparam *ring,
+			const bool fd_mode)
+{
+	u8 num_rx, num_tx;
+	u16 ram_free;
+
+	/* default CAN */
+
+	num_tx = config->tx.def[fd_mode];
+	num_tx = can_ram_rounddown_pow_of_two(config, &config->tx, num_tx);
+
+	ram_free = config->size;
+	ram_free -= config->tx.size[fd_mode] * num_tx;
+
+	num_rx = ram_free / config->rx.size[fd_mode];
+
+	layout->default_rx = can_ram_rounddown_pow_of_two(config, &config->rx, num_rx);
+	layout->default_tx = num_tx;
+
+	/* MAX CAN */
+
+	ram_free = config->size;
+	ram_free -= config->tx.size[fd_mode] * config->tx.min;
+	num_rx = ram_free / config->rx.size[fd_mode];
+
+	ram_free = config->size;
+	ram_free -= config->rx.size[fd_mode] * config->rx.min;
+	num_tx = ram_free / config->tx.size[fd_mode];
+
+	layout->max_rx = can_ram_rounddown_pow_of_two(config, &config->rx, num_rx);
+	layout->max_tx = can_ram_rounddown_pow_of_two(config, &config->tx, num_tx);
+
+	/* cur CAN */
+
+	if (ring) {
+		num_rx = can_ram_rounddown_pow_of_two(config, &config->rx, ring->rx_pending);
+
+		ram_free = config->size - config->rx.size[fd_mode] * num_rx;
+		num_tx = ram_free / config->tx.size[fd_mode];
+		num_tx = min_t(u8, ring->tx_pending, num_tx);
+		num_tx = can_ram_rounddown_pow_of_two(config, &config->tx, num_tx);
+
+		layout->cur_rx = num_rx;
+		layout->cur_tx = num_tx;
+	} else {
+		layout->cur_rx = layout->default_rx;
+		layout->cur_tx = layout->default_tx;
+	}
+}

drivers/net/can/spi/mcp251xfd/mcp251xfd-ram.h

@@ -0,0 +1,57 @@
+/* SPDX-License-Identifier: GPL-2.0
+ *
+ * mcp251xfd - Microchip MCP251xFD Family CAN controller driver
+ *
+ * Copyright (c) 2021, 2022 Pengutronix,
+ *               Marc Kleine-Budde <kernel@pengutronix.de>
+ */
+
+#ifndef _MCP251XFD_RAM_H
+#define _MCP251XFD_RAM_H
+
+#include <linux/ethtool.h>
+
+#define CAN_RAM_NUM_MAX (-1)
+
+enum can_ram_mode {
+	CAN_RAM_MODE_CAN,
+	CAN_RAM_MODE_CANFD,
+	__CAN_RAM_MODE_MAX
+};
+
+struct can_ram_obj_config {
+	u8 size[__CAN_RAM_MODE_MAX];
+
+	u8 def[__CAN_RAM_MODE_MAX];
+	u8 min;
+	u8 max;
+
+	u8 fifo_num;
+	u8 fifo_depth_min;
+};
+
+struct can_ram_config {
+	const struct can_ram_obj_config rx;
+	const struct can_ram_obj_config tx;
+
+	u16 size;
+	u8 fifo_depth;
+};
+
+struct can_ram_layout {
+	u8 default_rx;
+	u8 default_tx;
+
+	u8 max_rx;
+	u8 max_tx;
+
+	u8 cur_rx;
+	u8 cur_tx;
+};
+
+void can_ram_get_layout(struct can_ram_layout *layout,
+			const struct can_ram_config *config,
+			const struct ethtool_ringparam *ring,
+			const bool fd_mode);
+
+#endif