spi: aspeed: Adjust direct mapping to device size

The segment registers of the FMC/SPI controllers provide a way to
configure the mapping window of the flash device contents on the AHB
bus. Adjust this window to the size of the spi-mem mapping.

Things get more complex with multiple devices. The driver needs to
also adjust the window of the next device to make sure that there is
no overlap, even if there is no available device. The proposal below
is not perfect but it is covering all the cases we have seen on
different boards with one and two devices on the same bus.
Reviewed-by: Joel Stanley <joel@jms.id.au>
Tested-by: Joel Stanley <joel@jms.id.au>
Tested-by: Tao Ren <rentao.bupt@gmail.com>
Tested-by: Jae Hyun Yoo <quic_jaehyoo@quicinc.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Link: https://lore.kernel.org/r/20220509175616.1089346-6-clg@kaod.orgSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-aspeed-smc.c

@@ -411,6 +411,92 @@ static int aspeed_spi_chip_set_default_window(struct aspeed_spi_chip *chip)
 	return chip->ahb_window_size ? 0 : -1;
 }
 
+static int aspeed_spi_set_window(struct aspeed_spi *aspi,
+				 const struct aspeed_spi_window *win)
+{
+	u32 start = aspi->ahb_base_phy + win->offset;
+	u32 end = start + win->size;
+	void __iomem *seg_reg = aspi->regs + CE0_SEGMENT_ADDR_REG + win->cs * 4;
+	u32 seg_val_backup = readl(seg_reg);
+	u32 seg_val = aspi->data->segment_reg(aspi, start, end);
+
+	if (seg_val == seg_val_backup)
+		return 0;
+
+	writel(seg_val, seg_reg);
+
+	/*
+	 * Restore initial value if something goes wrong else we could
+	 * loose access to the chip.
+	 */
+	if (seg_val != readl(seg_reg)) {
+		dev_err(aspi->dev, "CE%d invalid window [ 0x%.8x - 0x%.8x ] %dMB",
+			win->cs, start, end - 1, win->size >> 20);
+		writel(seg_val_backup, seg_reg);
+		return -EIO;
+	}
+
+	if (win->size)
+		dev_dbg(aspi->dev, "CE%d new window [ 0x%.8x - 0x%.8x ] %dMB",
+			win->cs, start, end - 1,  win->size >> 20);
+	else
+		dev_dbg(aspi->dev, "CE%d window closed", win->cs);
+
+	return 0;
+}
+
+/*
+ * Yet to be done when possible :
+ * - Align mappings on flash size (we don't have the info)
+ * - ioremap each window, not strictly necessary since the overall window
+ *   is correct.
+ */
+static int aspeed_spi_chip_adjust_window(struct aspeed_spi_chip *chip,
+					 u32 local_offset, u32 size)
+{
+	struct aspeed_spi *aspi = chip->aspi;
+	struct aspeed_spi_window windows[ASPEED_SPI_MAX_NUM_CS] = { 0 };
+	struct aspeed_spi_window *win = &windows[chip->cs];
+	int ret;
+
+	aspeed_spi_get_windows(aspi, windows);
+
+	/* Adjust this chip window */
+	win->offset += local_offset;
+	win->size = size;
+
+	if (win->offset + win->size > aspi->ahb_window_size) {
+		win->size = aspi->ahb_window_size - win->offset;
+		dev_warn(aspi->dev, "CE%d window resized to %dMB", chip->cs, win->size >> 20);
+	}
+
+	ret = aspeed_spi_set_window(aspi, win);
+	if (ret)
+		return ret;
+
+	/* Update chip mapping info */
+	chip->ahb_base = aspi->ahb_base + win->offset;
+	chip->ahb_window_size = win->size;
+
+	/*
+	 * Also adjust next chip window to make sure that it does not
+	 * overlap with the current window.
+	 */
+	if (chip->cs < aspi->data->max_cs - 1) {
+		struct aspeed_spi_window *next = &windows[chip->cs + 1];
+
+		/* Change offset and size to keep the same end address */
+		if ((next->offset + next->size) > (win->offset + win->size))
+			next->size = (next->offset + next->size) - (win->offset + win->size);
+		else
+			next->size = 0;
+		next->offset = win->offset + win->size;
+
+		aspeed_spi_set_window(aspi, next);
+	}
+	return 0;
+}
+
 static int aspeed_spi_dirmap_create(struct spi_mem_dirmap_desc *desc)
 {
 	struct aspeed_spi *aspi = spi_controller_get_devdata(desc->mem->spi->master);
@@ -425,6 +511,8 @@ static int aspeed_spi_dirmap_create(struct spi_mem_dirmap_desc *desc)
 	if (op->data.dir != SPI_MEM_DATA_IN)
 		return -EOPNOTSUPP;
 
+	aspeed_spi_chip_adjust_window(chip, desc->info.offset, desc->info.length);
+
 	if (desc->info.length > chip->ahb_window_size)
 		dev_warn(aspi->dev, "CE%d window (%dMB) too small for mapping",
 			 chip->cs, chip->ahb_window_size >> 20);