[v3,2/2] spi: meson-spicc: Use pinctrl to drive CLK line when idle
Commit Message
Between SPI transactions, all SPI pins are in HiZ state. When using the SS
signal from the SPICC controller it's not an issue because when the
transaction resumes all pins come back to the right state at the same time
as SS.
The problem is when we use CS as a GPIO. In fact, between the GPIO CS
state change and SPI pins state change from idle, you can have a missing or
spurious clock transition.
Set a bias on the clock depending on the clock polarity requested before CS
goes active, by passing a special "idle-low" and "idle-high" pinctrl state
and setting the right state at a start of a message
Reported-by: Da Xue <da@libre.computer>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Amjad Ouled-Ameur <aouledameur@baylibre.com>
---
arch/arm64/boot/dts/amlogic/meson-gxl.dtsi | 14 +++++++++++
drivers/spi/spi-meson-spicc.c | 39 +++++++++++++++++++++++++++++-
2 files changed, 52 insertions(+), 1 deletion(-)
Comments
Hi Amjad,
On Wed, Oct 19, 2022 at 4:03 PM Amjad Ouled-Ameur
<aouledameur@baylibre.com> wrote:
[...]
> diff --git a/arch/arm64/boot/dts/amlogic/meson-gxl.dtsi b/arch/arm64/boot/dts/amlogic/meson-gxl.dtsi
> index c3ac531c4f84..04e9d0f1bde0 100644
> --- a/arch/arm64/boot/dts/amlogic/meson-gxl.dtsi
> +++ b/arch/arm64/boot/dts/amlogic/meson-gxl.dtsi
> @@ -429,6 +429,20 @@ mux {
> };
> };
>
> + spi_idle_high_pins: spi-idle-high-pins {
> + mux {
> + groups = "spi_sclk";
> + bias-pull-up;
> + };
> + };
> +
> + spi_idle_low_pins: spi-idle-low-pins {
> + mux {
> + groups = "spi_sclk";
> + bias-pull-down;
> + };
> + };
> +
We typically have the .dts{,i} changes in a separate patch. I suggest
doing the same here.
I also have two questions about this part:
- why are these not referenced by the SPICC controller node?
- is there a particular reason why meson-gxl.dtsi is updated but
meson-gxbb.dtsi is not? (my understanding is that GXBB is also lacking
hardware OEN support)
Best regards,
Martin
On 19/10/2022 22:50, Martin Blumenstingl wrote:
> Hi Amjad,
>
> On Wed, Oct 19, 2022 at 4:03 PM Amjad Ouled-Ameur
> <aouledameur@baylibre.com> wrote:
> [...]
>> diff --git a/arch/arm64/boot/dts/amlogic/meson-gxl.dtsi b/arch/arm64/boot/dts/amlogic/meson-gxl.dtsi
>> index c3ac531c4f84..04e9d0f1bde0 100644
>> --- a/arch/arm64/boot/dts/amlogic/meson-gxl.dtsi
>> +++ b/arch/arm64/boot/dts/amlogic/meson-gxl.dtsi
>> @@ -429,6 +429,20 @@ mux {
>> };
>> };
>>
>> + spi_idle_high_pins: spi-idle-high-pins {
>> + mux {
>> + groups = "spi_sclk";
>> + bias-pull-up;
>> + };
>> + };
>> +
>> + spi_idle_low_pins: spi-idle-low-pins {
>> + mux {
>> + groups = "spi_sclk";
>> + bias-pull-down;
>> + };
>> + };
>> +
> We typically have the .dts{,i} changes in a separate patch. I suggest
> doing the same here.
> I also have two questions about this part:
> - why are these not referenced by the SPICC controller node?
Because it's up to the board to use or not those states, if some pull-up/downs
are already present on the lines no need to use those special states.
> - is there a particular reason why meson-gxl.dtsi is updated but
> meson-gxbb.dtsi is not? (my understanding is that GXBB is also lacking
> hardware OEN support)
Good question indeed, so indeed they should be added in meson-gxbb.dtsi in a separate patch.
>
>
> Best regards,
> Martin
Thanks,
Neil
@@ -429,6 +429,20 @@ mux {
};
};
+ spi_idle_high_pins: spi-idle-high-pins {
+ mux {
+ groups = "spi_sclk";
+ bias-pull-up;
+ };
+ };
+
+ spi_idle_low_pins: spi-idle-low-pins {
+ mux {
+ groups = "spi_sclk";
+ bias-pull-down;
+ };
+ };
+
spi_ss0_pins: spi-ss0 {
mux {
groups = "spi_ss0";
@@ -21,6 +21,7 @@
#include <linux/types.h>
#include <linux/interrupt.h>
#include <linux/reset.h>
+#include <linux/pinctrl/consumer.h>
/*
* The Meson SPICC controller could support DMA based transfers, but is not
@@ -167,6 +168,9 @@ struct meson_spicc_device {
unsigned long tx_remain;
unsigned long rx_remain;
unsigned long xfer_remain;
+ struct pinctrl *pinctrl;
+ struct pinctrl_state *pins_idle_high;
+ struct pinctrl_state *pins_idle_low;
};
#define pow2_clk_to_spicc(_div) container_of(_div, struct meson_spicc_device, pow2_div)
@@ -175,8 +179,22 @@ static void meson_spicc_oen_enable(struct meson_spicc_device *spicc)
{
u32 conf;
- if (!spicc->data->has_oen)
+ if (!spicc->data->has_oen) {
+ /* Try to get pinctrl states for idle high/low */
+ spicc->pins_idle_high = pinctrl_lookup_state(spicc->pinctrl,
+ "idle-high");
+ if (IS_ERR(spicc->pins_idle_high)) {
+ dev_warn(&spicc->pdev->dev, "can't get idle-high pinctrl\n");
+ spicc->pins_idle_high = NULL;
+ }
+ spicc->pins_idle_low = pinctrl_lookup_state(spicc->pinctrl,
+ "idle-low");
+ if (IS_ERR(spicc->pins_idle_low)) {
+ dev_warn(&spicc->pdev->dev, "can't get idle-low pinctrl\n");
+ spicc->pins_idle_low = NULL;
+ }
return;
+ }
conf = readl_relaxed(spicc->base + SPICC_ENH_CTL0) |
SPICC_ENH_MOSI_OEN | SPICC_ENH_CLK_OEN | SPICC_ENH_CS_OEN;
@@ -441,6 +459,16 @@ static int meson_spicc_prepare_message(struct spi_master *master,
else
conf &= ~SPICC_POL;
+ if (!spicc->data->has_oen) {
+ if (spi->mode & SPI_CPOL) {
+ if (spicc->pins_idle_high)
+ pinctrl_select_state(spicc->pinctrl, spicc->pins_idle_high);
+ } else {
+ if (spicc->pins_idle_low)
+ pinctrl_select_state(spicc->pinctrl, spicc->pins_idle_low);
+ }
+ }
+
if (spi->mode & SPI_CPHA)
conf |= SPICC_PHA;
else
@@ -487,6 +515,9 @@ static int meson_spicc_unprepare_transfer(struct spi_master *master)
/* Set default configuration, keeping datarate field */
writel_relaxed(conf, spicc->base + SPICC_CONREG);
+ if (!spicc->data->has_oen)
+ pinctrl_select_default_state(&spicc->pdev->dev);
+
return 0;
}
@@ -798,6 +829,12 @@ static int meson_spicc_probe(struct platform_device *pdev)
goto out_core_clk;
}
+ spicc->pinctrl = devm_pinctrl_get(&pdev->dev);
+ if (IS_ERR(spicc->pinctrl)) {
+ ret = PTR_ERR(spicc->pinctrl);
+ goto out_clk;
+ }
+
device_reset_optional(&pdev->dev);
master->num_chipselect = 4;