From: Naidu Tellapati <naidu.tellapati@xxxxxxxxxx>
The PWM hardware on Pistachio platform has a maximum timebase steps
value to 255. To fix it, let's introduce a compatible-specific
data structure to contain the SoC-specific details and use it to
specify a maximum timebase.
Also, let's limit the minimum timebase to 16 steps, to allow a sane
range of duty cycle steps.
Fixes: 277bb6a29e00 ("pwm: Imagination Technologies PWM DAC driver")
Signed-off-by: Naidu Tellapati <naidu.tellapati@xxxxxxxxxx>
Signed-off-by: Ezequiel Garcia <ezequiel.garcia@xxxxxxxxxx>
---
This patch is needed for the pwm-img to work properly, so it should be
pushed as a v4.1-rc fix.
Changes from v1:
* After some investigation, we found the hardware has no lower limit
for the timebase. However, it still makes sense to have limit it,
to allow a sane duty cycle resolution. Updated the commit log and added
some comments to the driver explaining this.
* Minor style fixes.
drivers/pwm/pwm-img.c | 76 +++++++++++++++++++++++++++++++++++++++++++--------
1 file changed, 64 insertions(+), 12 deletions(-)
diff --git a/drivers/pwm/pwm-img.c b/drivers/pwm/pwm-img.c
index 476171a..8a029f9 100644
--- a/drivers/pwm/pwm-img.c
+++ b/drivers/pwm/pwm-img.c
@@ -16,6 +16,7 @@
#include <linux/mfd/syscon.h>
#include <linux/module.h>
#include <linux/of.h>
+#include <linux/of_device.h>
#include <linux/platform_device.h>
#include <linux/pwm.h>
#include <linux/regmap.h>
@@ -38,7 +39,22 @@
#define PERIP_PWM_PDM_CONTROL_CH_MASK 0x1
#define PERIP_PWM_PDM_CONTROL_CH_SHIFT(ch) ((ch) * 4)
-#define MAX_TMBASE_STEPS 65536
+/*
+ * PWM period is specified with a timebase register,
+ * in number of step periods. The PWM duty cycle is also
+ * specified in step periods, in the [0, $timebase] range.
+ * In other words, the timebase imposes the duty cycle
+ * resolution. Therefore, let's constraint the timebase to
+ * a minimum value to allow a sane range of duty cycle values.
+ * Imposing a minimum timebase, will impose a maximum PWM frequency.
+ *
+ * The value chosen is completely arbitrary.
+ */
+#define MIN_TMBASE_STEPS 16
+
+struct img_pwm_soc_data {
+ u32 max_timebase;
+};
struct img_pwm_chip {
struct device *dev;
@@ -47,6 +63,9 @@ struct img_pwm_chip {
struct clk *sys_clk;
void __iomem *base;
struct regmap *periph_regs;
+ int max_period_ns;
+ int min_period_ns;
+ const struct img_pwm_soc_data *data;
};
static inline struct img_pwm_chip *to_img_pwm_chip(struct pwm_chip *chip)
@@ -72,24 +91,31 @@ static int img_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
u32 val, div, duty, timebase;
unsigned long mul, output_clk_hz, input_clk_hz;
struct img_pwm_chip *pwm_chip = to_img_pwm_chip(chip);
+ unsigned int max_timebase = pwm_chip->data->max_timebase;
+
+ if (period_ns < pwm_chip->min_period_ns ||
+ period_ns > pwm_chip->max_period_ns) {
+ dev_err(chip->dev, "configured period not in range\n");
+ return -ERANGE;
+ }
input_clk_hz = clk_get_rate(pwm_chip->pwm_clk);
output_clk_hz = DIV_ROUND_UP(NSEC_PER_SEC, period_ns);
mul = DIV_ROUND_UP(input_clk_hz, output_clk_hz);
- if (mul <= MAX_TMBASE_STEPS) {
+ if (mul <= max_timebase) {
div = PWM_CTRL_CFG_NO_SUB_DIV;
timebase = DIV_ROUND_UP(mul, 1);
- } else if (mul <= MAX_TMBASE_STEPS * 8) {
+ } else if (mul <= max_timebase * 8) {
div = PWM_CTRL_CFG_SUB_DIV0;
timebase = DIV_ROUND_UP(mul, 8);
- } else if (mul <= MAX_TMBASE_STEPS * 64) {
+ } else if (mul <= max_timebase * 64) {
div = PWM_CTRL_CFG_SUB_DIV1;
timebase = DIV_ROUND_UP(mul, 64);
- } else if (mul <= MAX_TMBASE_STEPS * 512) {
+ } else if (mul <= max_timebase * 512) {
div = PWM_CTRL_CFG_SUB_DIV0_DIV1;
timebase = DIV_ROUND_UP(mul, 512);
- } else if (mul > MAX_TMBASE_STEPS * 512) {
+ } else if (mul > max_timebase * 512) {
dev_err(chip->dev,
"failed to configure timebase steps/divider value\n");
return -EINVAL;
@@ -143,11 +169,27 @@ static const struct pwm_ops img_pwm_ops = {
.owner = THIS_MODULE,
};
+static const struct img_pwm_soc_data pistachio_pwm = {
+ .max_timebase = 255,
+};
+
+static const struct of_device_id img_pwm_of_match[] = {
+ {
+ .compatible = "img,pistachio-pwm",
+ .data = &pistachio_pwm,
+ },
+ { }
+};
+MODULE_DEVICE_TABLE(of, img_pwm_of_match);
+
static int img_pwm_probe(struct platform_device *pdev)
{
int ret;
+ u64 val;
+ unsigned long clk_rate;
struct resource *res;
struct img_pwm_chip *pwm;
+ const struct of_device_id *of_dev_id;
pwm = devm_kzalloc(&pdev->dev, sizeof(*pwm), GFP_KERNEL);
if (!pwm)
@@ -160,6 +202,11 @@ static int img_pwm_probe(struct platform_device *pdev)
if (IS_ERR(pwm->base))
return PTR_ERR(pwm->base);
+ of_dev_id = of_match_device(img_pwm_of_match, &pdev->dev);
+ if (!of_dev_id)
+ return -ENODEV;
+ pwm->data = of_dev_id->data;
+
pwm->periph_regs = syscon_regmap_lookup_by_phandle(pdev->dev.of_node,
"img,cr-periph");
if (IS_ERR(pwm->periph_regs))
@@ -189,6 +236,17 @@ static int img_pwm_probe(struct platform_device *pdev)
goto disable_sysclk;
}
+ clk_rate = clk_get_rate(pwm->pwm_clk);
+
+ /* The maximum input clock divider is 512 */
+ val = (u64)NSEC_PER_SEC * 512 * pwm->data->max_timebase;
+ do_div(val, clk_rate);
+ pwm->max_period_ns = val;
+
+ val = (u64)NSEC_PER_SEC * MIN_TMBASE_STEPS;
+ do_div(val, clk_rate);
+ pwm->min_period_ns = val;
+
pwm->chip.dev = &pdev->dev;
pwm->chip.ops = &img_pwm_ops;
pwm->chip.base = -1;
@@ -228,12 +286,6 @@ static int img_pwm_remove(struct platform_device *pdev)
return pwmchip_remove(&pwm_chip->chip);
}
-static const struct of_device_id img_pwm_of_match[] = {
- { .compatible = "img,pistachio-pwm", },
- { }
-};
-MODULE_DEVICE_TABLE(of, img_pwm_of_match);
-
static struct platform_driver img_pwm_driver = {
.driver = {
.name = "img-pwm",
--
2.3.3
