Hello, [replaced Andrzej Hajda's email address with his new one]
On Wed, Sep 29, 2021 at 10:05:57PM -0500, Bjorn Andersson wrote: > The SN65DSI86 provides the ability to supply a PWM signal on GPIO 4, > with the primary purpose of controlling the backlight of the attached > panel. Add an implementation that exposes this using the standard PWM > framework, to allow e.g. pwm-backlight to expose this to the user. Sorry for the long delay in reviewing this. > Signed-off-by: Bjorn Andersson <bjorn.anders...@linaro.org> > --- > > Changes since v5: > - Make ti_sn65dsi86_read_u16() use regmap_bulk_read() > - Update the wording related to the formula for the period being wrong to not > just say I'm "assuming because it's easier". > - Updated comment related to minimum period > - Clamp duty <= period in get_state() > > drivers/gpu/drm/bridge/ti-sn65dsi86.c | 366 +++++++++++++++++++++++++- > 1 file changed, 360 insertions(+), 6 deletions(-) > > diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c > b/drivers/gpu/drm/bridge/ti-sn65dsi86.c > index 412fb6f564ea..ccf6496cc9ff 100644 > --- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c > +++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c > @@ -4,7 +4,9 @@ > * datasheet: https://www.ti.com/lit/ds/symlink/sn65dsi86.pdf > */ > > +#include <linux/atomic.h> > #include <linux/auxiliary_bus.h> > +#include <linux/bitfield.h> > #include <linux/bits.h> > #include <linux/clk.h> > #include <linux/debugfs.h> > @@ -15,6 +17,7 @@ > #include <linux/module.h> > #include <linux/of_graph.h> > #include <linux/pm_runtime.h> > +#include <linux/pwm.h> > #include <linux/regmap.h> > #include <linux/regulator/consumer.h> > > @@ -91,6 +94,13 @@ > #define SN_ML_TX_MODE_REG 0x96 > #define ML_TX_MAIN_LINK_OFF 0 > #define ML_TX_NORMAL_MODE BIT(0) > +#define SN_PWM_PRE_DIV_REG 0xA0 > +#define SN_BACKLIGHT_SCALE_REG 0xA1 > +#define BACKLIGHT_SCALE_MAX 0xFFFF > +#define SN_BACKLIGHT_REG 0xA3 > +#define SN_PWM_EN_INV_REG 0xA5 > +#define SN_PWM_INV_MASK BIT(0) > +#define SN_PWM_EN_MASK BIT(1) > #define SN_AUX_CMD_STATUS_REG 0xF4 > #define AUX_IRQ_STATUS_AUX_RPLY_TOUT BIT(3) > #define AUX_IRQ_STATUS_AUX_SHORT BIT(5) > @@ -113,11 +123,14 @@ > > #define SN_LINK_TRAINING_TRIES 10 > > +#define SN_PWM_GPIO_IDX 3 /* 4th GPIO */ > + > /** > * struct ti_sn65dsi86 - Platform data for ti-sn65dsi86 driver. > * @bridge_aux: AUX-bus sub device for MIPI-to-eDP bridge functionality. > * @gpio_aux: AUX-bus sub device for GPIO controller functionality. > * @aux_aux: AUX-bus sub device for eDP AUX channel functionality. > + * @pwm_aux: AUX-bus sub device for PWM controller functionality. > * > * @dev: Pointer to the top level (i2c) device. > * @regmap: Regmap for accessing i2c. > @@ -145,11 +158,17 @@ > * bitmap so we can do atomic ops on it without an extra > * lock so concurrent users of our 4 GPIOs don't stomp on > * each other's read-modify-write. > + * > + * @pchip: pwm_chip if the PWM is exposed. > + * @pwm_enabled: Used to track if the PWM signal is currently enabled. > + * @pwm_pin_busy: Track if GPIO4 is currently requested for GPIO or PWM. > + * @pwm_refclk_freq: Cache for the reference clock input to the PWM. > */ > struct ti_sn65dsi86 { > struct auxiliary_device bridge_aux; > struct auxiliary_device gpio_aux; > struct auxiliary_device aux_aux; > + struct auxiliary_device pwm_aux; > > struct device *dev; > struct regmap *regmap; > @@ -172,6 +191,12 @@ struct ti_sn65dsi86 { > struct gpio_chip gchip; > DECLARE_BITMAP(gchip_output, SN_NUM_GPIOS); > #endif > +#if defined(CONFIG_PWM) > + struct pwm_chip pchip; > + bool pwm_enabled; > + atomic_t pwm_pin_busy; > +#endif > + unsigned int pwm_refclk_freq; > }; > > static const struct regmap_range ti_sn65dsi86_volatile_ranges[] = { > @@ -190,6 +215,21 @@ static const struct regmap_config > ti_sn65dsi86_regmap_config = { > .cache_type = REGCACHE_NONE, > }; > > +static int ti_sn65dsi86_read_u16(struct ti_sn65dsi86 *pdata, > + unsigned int reg, u16 *val) > +{ > + u8 buf[2]; > + int ret; > + > + ret = regmap_bulk_read(pdata->regmap, reg, buf, ARRAY_SIZE(buf)); > + if (ret) > + return ret; > + > + *val = buf[0] | (buf[1] << 8); > + > + return 0; > +} > + > static void ti_sn65dsi86_write_u16(struct ti_sn65dsi86 *pdata, > unsigned int reg, u16 val) > { > @@ -254,6 +294,12 @@ static void ti_sn_bridge_set_refclk_freq(struct > ti_sn65dsi86 *pdata) > > regmap_update_bits(pdata->regmap, SN_DPPLL_SRC_REG, REFCLK_FREQ_MASK, > REFCLK_FREQ(i)); > + > + /* > + * The PWM refclk is based on the value written to SN_DPPLL_SRC_REG, > + * regardless of its actual sourcing. > + */ > + pdata->pwm_refclk_freq = ti_sn_bridge_refclk_lut[i]; > } > > static void ti_sn65dsi86_enable_comms(struct ti_sn65dsi86 *pdata) > @@ -1260,9 +1306,289 @@ static struct auxiliary_driver ti_sn_bridge_driver = { > }; > > /* > ----------------------------------------------------------------------------- > - * GPIO Controller > + * PWM Controller > */ > +#if defined(CONFIG_PWM) > +static int ti_sn_pwm_pin_request(struct ti_sn65dsi86 *pdata) > +{ > + return atomic_xchg(&pdata->pwm_pin_busy, 1) ? -EBUSY : 0; > +} > + > +static void ti_sn_pwm_pin_release(struct ti_sn65dsi86 *pdata) > +{ > + atomic_set(&pdata->pwm_pin_busy, 0); > +} > + > +static struct ti_sn65dsi86 *pwm_chip_to_ti_sn_bridge(struct pwm_chip *chip) > +{ > + return container_of(chip, struct ti_sn65dsi86, pchip); > +} > + > +static int ti_sn_pwm_request(struct pwm_chip *chip, struct pwm_device *pwm) > +{ > + struct ti_sn65dsi86 *pdata = pwm_chip_to_ti_sn_bridge(chip); > > + return ti_sn_pwm_pin_request(pdata); > +} > + > +static void ti_sn_pwm_free(struct pwm_chip *chip, struct pwm_device *pwm) > +{ > + struct ti_sn65dsi86 *pdata = pwm_chip_to_ti_sn_bridge(chip); > + > + ti_sn_pwm_pin_release(pdata); > +} > + > +/* > + * Limitations: > + * - The PWM signal is not driven when the chip is powered down, or in its > + * reset state and the driver does not implement the "suspend state" > + * described in the documentation. In order to save power, state->enabled > is > + * interpreted as denoting if the signal is expected to be valid, and is > used > + * to determine if the chip needs to be kept powered. > + * - Changing both period and duty_cycle is not done atomically, neither is > the > + * multi-byte register updates, so the output might briefly be undefined > + * during update. > + */ > +static int ti_sn_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm, > + const struct pwm_state *state) > +{ > + struct ti_sn65dsi86 *pdata = pwm_chip_to_ti_sn_bridge(chip); > + unsigned int pwm_en_inv; > + unsigned int backlight; > + unsigned int pre_div; > + unsigned int scale; > + u64 period_max; > + u64 period; > + int ret; > + > + if (!pdata->pwm_enabled) { > + ret = pm_runtime_get_sync(pdata->dev); > + if (ret < 0) { > + pm_runtime_put_sync(pdata->dev); > + return ret; > + } > + } > + > + if (state->enabled) { > + if (!pdata->pwm_enabled) { > + /* > + * The chip might have been powered down while we > + * didn't hold a PM runtime reference, so mux in the > + * PWM function on the GPIO pin again. > + */ > + ret = regmap_update_bits(pdata->regmap, > SN_GPIO_CTRL_REG, > + SN_GPIO_MUX_MASK << (2 * > SN_PWM_GPIO_IDX), > + SN_GPIO_MUX_SPECIAL << (2 * > SN_PWM_GPIO_IDX)); > + if (ret) { > + dev_err(pdata->dev, "failed to mux in PWM > function\n"); > + goto out; > + } > + } > + > + /* > + * Per the datasheet the PWM frequency is given by: > + * > + * REFCLK_FREQ > + * PWM_FREQ = ----------------------------------- > + * PWM_PRE_DIV * BACKLIGHT_SCALE + 1 > + * > + * However, after careful review the author is convinced that > + * the documentation has lost some parenthesis around > + * "BACKLIGHT_SCALE + 1". > + * With that the formula can be written: > + * > + * T_pwm * REFCLK_FREQ = PWM_PRE_DIV * (BACKLIGHT_SCALE + 1) For my understanding: T_pwm = period length = 1 / PWM_FREQ, right? Maybe it's a good idea to state this more explicitly? > + * In order to keep BACKLIGHT_SCALE within its 16 bits, > + * PWM_PRE_DIV must be: > + * > + * T_pwm * REFCLK_FREQ > + * PWM_PRE_DIV >= ------------------------- > + * BACKLIGHT_SCALE_MAX + 1 > + * > + * To simplify the search and to favour higher resolution of > + * the duty cycle over accuracy of the period, the lowest > + * possible PWM_PRE_DIV is used. Finally the scale is > + * calculated as: > + * > + * T_pwm * REFCLK_FREQ > + * BACKLIGHT_SCALE = ---------------------- - 1 > + * PWM_PRE_DIV > + * > + * Here T_pwm is represented in seconds, so appropriate scaling > + * to nanoseconds is necessary. > + */ > + > + /* Minimum T_pwm is 1 / REFCLK_FREQ */ > + if (state->period <= NSEC_PER_SEC / pdata->pwm_refclk_freq) { > + ret = -EINVAL; > + goto out; > + } > + > + /* > + * Maximum T_pwm is 255 * (65535 + 1) / REFCLK_FREQ > + * Limit period to this to avoid overflows > + */ > + period_max = div_u64((u64)NSEC_PER_SEC * 255 * (65535 + 1), > + pdata->pwm_refclk_freq); > + if (period > period_max) period is uninitialized here. This must be if (state->period > period_max) . Alternatively to the if you could use period = min(state->period, period_max); Apart from this I'm happy with your patch set now. > + period = period_max; > + else > + period = state->period; > + > + pre_div = DIV64_U64_ROUND_UP(period * pdata->pwm_refclk_freq, > + (u64)NSEC_PER_SEC * > (BACKLIGHT_SCALE_MAX + 1)); > + scale = div64_u64(period * pdata->pwm_refclk_freq, > (u64)NSEC_PER_SEC * pre_div) - 1; After thinking a while about this---I think I stumbled about this calculation already in earlier revisions of this patch set---I think I now understood it. I never saw something like this before because other drivers with similar HW conditions would pick: pre_div = div64_u64(period * pdata->pwm_refclk_freq, (u64)NSEC_PER_SEC * (BACKLIGHT_SCALE_MAX + 1)); and then scale = BACKLIGHT_SCALE_MAX. This latter approach weights high resolution of duty_cycle still higher over period exactness than your approach. For me both approaches are fine. Best regards Uwe -- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | https://www.pengutronix.de/ |
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