Commit 76b17e6e authored by Julius Werner's avatar Julius Werner Committed by Mark Brown
Browse files

spi/rockchip: Add device tree property to configure Rx Sample Delay 



We have found that we can sometimes see read failures on boards with
high-capacitance SPI lines. It seems that the controller samples the Rx
data line too early, and its register interface has an "Rx Sample Delay"
setting to fine-tune against this issue.

This patch adds a new optional device tree entry that can configure this
delay in terms of nanoseconds. The kernel will calculate the
best-fitting amount of parent clock ticks to program the controller with
based on that.

Signed-off-by: default avatarJulius Werner <jwerner@chromium.org>
Signed-off-by: default avatarMark Brown <broonie@kernel.org>
parent 2291793c

Documentation/devicetree/bindings/spi/spi-rockchip.txt

+4 −0
Original line number Diff line number Diff line
@@ -24,6 +24,9 @@ Optional Properties: 
- dmas: DMA specifiers for tx and rx dma. See the DMA client binding,

		Documentation/devicetree/bindings/dma/dma.txt

- dma-names: DMA request names should include "tx" and "rx" if present.

- rx-sample-delay-ns: nanoseconds to delay after the SCLK edge before sampling

		Rx data (may need to be fine tuned for high capacitance lines).

		No delay (0) by default.





Example:
@@ -33,6 +36,7 @@ Example: 
		reg = <0xff110000 0x1000>;

		dmas = <&pdma1 11>, <&pdma1 12>;

		dma-names = "tx", "rx";

		rx-sample-delay-ns = <10>;

		#address-cells = <1>;

		#size-cells = <0>;

		interrupts = <GIC_SPI 44 IRQ_TYPE_LEVEL_HIGH>;

drivers/spi/spi-rockchip.c

+21 −0
Original line number Diff line number Diff line
@@ -179,6 +179,7 @@ struct rockchip_spi { 
	u8 tmode;

	u8 bpw;

	u8 n_bytes;

	u8 rsd_nsecs;

	unsigned len;

	u32 speed;
@@ -499,6 +500,7 @@ static void rockchip_spi_config(struct rockchip_spi *rs) 
{

	u32 div = 0;

	u32 dmacr = 0;

	int rsd = 0;



	u32 cr0 = (CR0_BHT_8BIT << CR0_BHT_OFFSET)

		| (CR0_SSD_ONE << CR0_SSD_OFFSET);
@@ -528,6 +530,20 @@ static void rockchip_spi_config(struct rockchip_spi *rs) 
	div = max_t(u32, rs->max_freq / rs->speed, 1);

	div = (div + 1) & 0xfffe;



	/* Rx sample delay is expressed in parent clock cycles (max 3) */

	rsd = DIV_ROUND_CLOSEST(rs->rsd_nsecs * (rs->max_freq >> 8),

				1000000000 >> 8);

	if (!rsd && rs->rsd_nsecs) {

		pr_warn_once("rockchip-spi: %u Hz are too slow to express %u ns delay\n",

			     rs->max_freq, rs->rsd_nsecs);

	} else if (rsd > 3) {

		rsd = 3;

		pr_warn_once("rockchip-spi: %u Hz are too fast to express %u ns delay, clamping at %u ns\n",

			     rs->max_freq, rs->rsd_nsecs,

			     rsd * 1000000000U / rs->max_freq);

	}

	cr0 |= rsd << CR0_RSD_OFFSET;



	writel_relaxed(cr0, rs->regs + ROCKCHIP_SPI_CTRLR0);



	writel_relaxed(rs->len - 1, rs->regs + ROCKCHIP_SPI_CTRLR1);
@@ -620,6 +636,7 @@ static int rockchip_spi_probe(struct platform_device *pdev) 
	struct rockchip_spi *rs;

	struct spi_master *master;

	struct resource *mem;

	u32 rsd_nsecs;



	master = spi_alloc_master(&pdev->dev, sizeof(struct rockchip_spi));

	if (!master)
@@ -671,6 +688,10 @@ static int rockchip_spi_probe(struct platform_device *pdev) 
	rs->dev = &pdev->dev;

	rs->max_freq = clk_get_rate(rs->spiclk);



	if (!of_property_read_u32(pdev->dev.of_node, "rx-sample-delay-ns",

				  &rsd_nsecs))

		rs->rsd_nsecs = rsd_nsecs;



	rs->fifo_len = get_fifo_len(rs);

	if (!rs->fifo_len) {

		dev_err(&pdev->dev, "Failed to get fifo length\n");

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