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: Julius Werner <jwer...@chromium.org>
---
.../devicetree/bindings/spi/spi-rockchip.txt | 4 ++++
drivers/spi/spi-rockchip.c | 21 +++++++++++++++++++++
2 files changed, 25 insertions(+)
diff --git a/Documentation/devicetree/bindings/spi/spi-rockchip.txt
b/Documentation/devicetree/bindings/spi/spi-rockchip.txt
index 467dec4..0c491bd 100644
--- a/Documentation/devicetree/bindings/spi/spi-rockchip.txt
+++ b/Documentation/devicetree/bindings/spi/spi-rockchip.txt
@@ -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>;
diff --git a/drivers/spi/spi-rockchip.c b/drivers/spi/spi-rockchip.c
index 5e4e52c..f89cd5d 100644
--- a/drivers/spi/spi-rockchip.c
+++ b/drivers/spi/spi-rockchip.c
@@ -179,6 +179,7 @@ struct rockchip_spi {
u8 tmode;
u8 bpw;
u8 n_bytes;
+ u8 rsd_nsecs;
unsigned len;
u32 speed;
@@ -493,6 +494,7 @@ 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);
@@ -522,6 +524,20 @@ static void rockchip_spi_config(struct rockchip_spi *rs)
div = DIV_ROUND_UP(rs->max_freq, rs->speed);
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);
@@ -614,6 +630,7 @@ 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)
@@ -665,6 +682,10 @@ 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");
--
2.1.2
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