[PATCH v2 2/4] spi: sg2044-nor: Honor SPI clock limits

[Han Gao]

The fixed divider ignores device and operation clock limits. Calculate
the divider before each transfer so SCK does not exceed either limit.

Advertise the controller maximum speed so the SPI core supplies a default
when the device omits its maximum speed. Use the fastest divider when no
speed limit is supplied.

Fixes: de16c322eefb ("spi: sophgo: add SG2044 SPI NOR controller driver")
Signed-off-by: Han Gao <gaohan at iscas.ac.cn>
---
 drivers/spi/spi-sg2044-nor.c | 39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

diff --git a/drivers/spi/spi-sg2044-nor.c b/drivers/spi/spi-sg2044-nor.c
index ff026ca0f76635fee959d7502f457d43dbec0706..bc9a8ee9bce448ccb2cad63f83ce54e30cbb0ea8 100644
--- a/drivers/spi/spi-sg2044-nor.c
+++ b/drivers/spi/spi-sg2044-nor.c
@@ -385,6 +385,29 @@ static ssize_t sg2044_spifmc_trans_reg(struct sg2044_spifmc *spifmc,
 	return 0;
 }
 
+static int sg2044_spifmc_set_speed(struct sg2044_spifmc *spifmc,
+				   unsigned int speed_hz)
+{
+	unsigned long rate = clk_get_rate(spifmc->clk);
+	u64 div;
+	u32 reg;
+
+	if (!rate)
+		return -EINVAL;
+
+	/* SCK = HCLK / (2 * (SckDiv + 1)); round down the resulting SCK. */
+	div = speed_hz ? DIV_ROUND_UP_ULL(rate, 2ULL * speed_hz) : 1;
+	if (div > SPIFMC_CTRL_SCK_DIV_MASK + 1)
+		return -EINVAL;
+
+	reg = readl(spifmc->io_base + SPIFMC_CTRL);
+	reg &= ~SPIFMC_CTRL_SCK_DIV_MASK;
+	reg |= div - 1;
+	writel(reg, spifmc->io_base + SPIFMC_CTRL);
+
+	return 0;
+}
+
 static int sg2044_spifmc_exec_op(struct spi_mem *mem,
 				 const struct spi_mem_op *op)
 {
@@ -395,11 +418,18 @@ static int sg2044_spifmc_exec_op(struct spi_mem *mem,
 
 	mutex_lock(&spifmc->lock);
 
+	ret = sg2044_spifmc_set_speed(spifmc, op->max_freq ?
+				    min(op->max_freq, mem->spi->max_speed_hz) :
+				    mem->spi->max_speed_hz);
+	if (ret)
+		goto out_unlock;
+
 	if (op->addr.nbytes == 0)
 		ret = sg2044_spifmc_trans_reg(spifmc, op);
 	else
 		ret = sg2044_spifmc_trans(spifmc, op);
 
+out_unlock:
 	mutex_unlock(&spifmc->lock);
 
 	return ret;
@@ -409,6 +439,10 @@ static const struct spi_controller_mem_ops sg2044_spifmc_mem_ops = {
 	.exec_op = sg2044_spifmc_exec_op,
 };
 
+static const struct spi_controller_mem_caps sg2044_spifmc_mem_caps = {
+	.per_op_freq = true,
+};
+
 static void sg2044_spifmc_init(struct sg2044_spifmc *spifmc)
 {
 	u32 tran_csr;
@@ -448,6 +482,10 @@ static int sg2044_spifmc_probe(struct platform_device *pdev)
 	if (IS_ERR(spifmc->clk))
 		return dev_err_probe(dev, PTR_ERR(spifmc->clk), "Cannot get and enable AHB clock\n");
 
+	ctrl->max_speed_hz = clk_get_rate(spifmc->clk) / 2;
+	if (!ctrl->max_speed_hz)
+		return dev_err_probe(dev, -EINVAL, "Invalid AHB clock rate\n");
+
 	spifmc->dev = &pdev->dev;
 	spifmc->ctrl = ctrl;
 
@@ -459,6 +497,7 @@ static int sg2044_spifmc_probe(struct platform_device *pdev)
 	ctrl->bits_per_word_mask = SPI_BPW_MASK(8);
 	ctrl->auto_runtime_pm = false;
 	ctrl->mem_ops = &sg2044_spifmc_mem_ops;
+	ctrl->mem_caps = &sg2044_spifmc_mem_caps;
 	ctrl->mode_bits = SPI_RX_DUAL | SPI_TX_DUAL | SPI_RX_QUAD | SPI_TX_QUAD;
 
 	ret = devm_mutex_init(dev, &spifmc->lock);

-- 
2.47.3