Re: [PATCH v2 2/3] media: camss: use v4l2_get_link_freq() to calculate the relevant clocks

From: Andrey Konovalov
Date: Thu Feb 18 2021 - 06:21:19 EST

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In reply to: Jacopo Mondi: "Re: [PATCH v2 2/3] media: camss: use v4l2_get_link_freq() to calculate the relevant clocks"
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Hi Jacopo,

On 18.02.2021 11:07, Jacopo Mondi wrote:

Hi Andrey,

On Thu, Feb 18, 2021 at 01:11:33AM +0300, Andrey Konovalov wrote:

There are places in the camss driver where camss_get_pixel_clock() is
called to get the pixel rate (using V4L2_CID_PIXEL_RATE control) and to
calculate the link frequency from it. There is a case when this would
not work: when V4L2_CID_PIXEL_RATE gets the rate at which the pixels are
read (sampled) from the sensor's pixel array, and this rate is different
from the pixel transmission rate over the CSI link, the link frequency
value can't be calculated from the pixel rate. One needs to use
V4L2_CID_LINK_FREQ to get the link frequency in this case.

Replace such calls to camss_get_pixel_clock() with calls to a wrapper
around v4l2_get_link_freq(). v4l2_get_link_freq() tries V4L2_CID_LINK_FREQ
first, and if it is not implemented by the camera sensor driver, falls
back to V4L2_CID_PIXEL_RATE to calculate the link frequency value from.

That's nice

Calls to camss_get_pixel_clock() from vfe_[check,set]_clock_rates()
are left intact as it looks like this VFE clock does depend on the
rate the pixel samples comes out of the camera sensor, not on the
frequency at which the link between the sensor and the CSI receiver
operates.

Out of curiosity, you have any idea why this happens ?

Unfortunately no.
There are no any details in the public datasheet on that - just
the formula itself (less than 1 line of text).

The patch looks good, fwiw given I don't know the platform:
Reviewed-by: Jacopo Mondi <jacopo@xxxxxxxxxx>

Thanks!

-- Andrey

Thanks
j

Signed-off-by: Andrey Konovalov <andrey.konovalov@xxxxxxxxxx>
Acked-by: Robert Foss <robert.foss@xxxxxxxxxx>
---
.../media/platform/qcom/camss/camss-csid.c | 20 +++++------
.../qcom/camss/camss-csiphy-2ph-1-0.c | 22 ++++++------
.../qcom/camss/camss-csiphy-3ph-1-0.c | 22 ++++++------
.../media/platform/qcom/camss/camss-csiphy.c | 36 +++++++++----------
.../media/platform/qcom/camss/camss-csiphy.h | 2 +-
drivers/media/platform/qcom/camss/camss.c | 23 ++++++++++++
drivers/media/platform/qcom/camss/camss.h | 2 ++
7 files changed, 71 insertions(+), 56 deletions(-)

diff --git a/drivers/media/platform/qcom/camss/camss-csid.c b/drivers/media/platform/qcom/camss/camss-csid.c
index be3fe76f3dc3..cff9759c9158 100644
--- a/drivers/media/platform/qcom/camss/camss-csid.c
+++ b/drivers/media/platform/qcom/camss/camss-csid.c
@@ -462,13 +462,17 @@ static irqreturn_t csid_isr(int irq, void *dev)
static int csid_set_clock_rates(struct csid_device *csid)
{
struct device *dev = csid->camss->dev;
- u32 pixel_clock;
+ const struct csid_format *fmt;
+ s64 link_freq;
int i, j;
int ret;

- ret = camss_get_pixel_clock(&csid->subdev.entity, &pixel_clock);
- if (ret)
- pixel_clock = 0;
+ fmt = csid_get_fmt_entry(csid->formats, csid->nformats,
+ csid->fmt[MSM_CSIPHY_PAD_SINK].code);
+ link_freq = camss_get_link_freq(&csid->subdev.entity, fmt->bpp,
+ csid->phy.lane_cnt);
+ if (link_freq < 0)
+ link_freq = 0;

for (i = 0; i < csid->nclocks; i++) {
struct camss_clock *clock = &csid->clock[i];
@@ -477,13 +481,7 @@ static int csid_set_clock_rates(struct csid_device *csid)
!strcmp(clock->name, "csi1") ||
!strcmp(clock->name, "csi2") ||
!strcmp(clock->name, "csi3")) {
- const struct csid_format *f = csid_get_fmt_entry(
- csid->formats,
- csid->nformats,
- csid->fmt[MSM_CSIPHY_PAD_SINK].code);
- u8 num_lanes = csid->phy.lane_cnt;
- u64 min_rate = pixel_clock * f->bpp /
- (2 * num_lanes * 4);
+ u64 min_rate = link_freq / 4;
long rate;

camss_add_clock_margin(&min_rate);
diff --git a/drivers/media/platform/qcom/camss/camss-csiphy-2ph-1-0.c b/drivers/media/platform/qcom/camss/camss-csiphy-2ph-1-0.c
index 12bce391d71f..30b454c369ab 100644
--- a/drivers/media/platform/qcom/camss/camss-csiphy-2ph-1-0.c
+++ b/drivers/media/platform/qcom/camss/camss-csiphy-2ph-1-0.c
@@ -51,16 +51,13 @@ static void csiphy_reset(struct csiphy_device *csiphy)
*
* Helper function to calculate settle count value. This is
* based on the CSI2 T_hs_settle parameter which in turn
- * is calculated based on the CSI2 transmitter pixel clock
- * frequency.
+ * is calculated based on the CSI2 transmitter link frequency.
*
- * Return settle count value or 0 if the CSI2 pixel clock
- * frequency is not available
+ * Return settle count value or 0 if the CSI2 link frequency
+ * is not available
*/
-static u8 csiphy_settle_cnt_calc(u32 pixel_clock, u8 bpp, u8 num_lanes,
- u32 timer_clk_rate)
+static u8 csiphy_settle_cnt_calc(s64 link_freq, u32 timer_clk_rate)
{
- u32 mipi_clock; /* Hz */
u32 ui; /* ps */
u32 timer_period; /* ps */
u32 t_hs_prepare_max; /* ps */
@@ -68,8 +65,10 @@ static u8 csiphy_settle_cnt_calc(u32 pixel_clock, u8 bpp, u8 num_lanes,
u32 t_hs_settle; /* ps */
u8 settle_cnt;

- mipi_clock = pixel_clock * bpp / (2 * num_lanes);
- ui = div_u64(1000000000000LL, mipi_clock);
+ if (link_freq <= 0)
+ return 0;
+
+ ui = div_u64(1000000000000LL, link_freq);
ui /= 2;
t_hs_prepare_max = 85000 + 6 * ui;
t_hs_prepare_zero_min = 145000 + 10 * ui;
@@ -83,15 +82,14 @@ static u8 csiphy_settle_cnt_calc(u32 pixel_clock, u8 bpp, u8 num_lanes,

static void csiphy_lanes_enable(struct csiphy_device *csiphy,
struct csiphy_config *cfg,
- u32 pixel_clock, u8 bpp, u8 lane_mask)
+ s64 link_freq, u8 lane_mask)
{
struct csiphy_lanes_cfg *c = &cfg->csi2->lane_cfg;
u8 settle_cnt;
u8 val, l = 0;
int i = 0;

- settle_cnt = csiphy_settle_cnt_calc(pixel_clock, bpp, c->num_data,
- csiphy->timer_clk_rate);
+ settle_cnt = csiphy_settle_cnt_calc(link_freq, csiphy->timer_clk_rate);

writel_relaxed(0x1, csiphy->base +
CAMSS_CSI_PHY_GLBL_T_INIT_CFG0);
diff --git a/drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c b/drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c
index 97cb9de85031..da7c3d3f9a10 100644
--- a/drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c
+++ b/drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c
@@ -107,24 +107,23 @@ static irqreturn_t csiphy_isr(int irq, void *dev)
*
* Helper function to calculate settle count value. This is
* based on the CSI2 T_hs_settle parameter which in turn
- * is calculated based on the CSI2 transmitter pixel clock
- * frequency.
+ * is calculated based on the CSI2 transmitter link frequency.
*
- * Return settle count value or 0 if the CSI2 pixel clock
- * frequency is not available
+ * Return settle count value or 0 if the CSI2 link frequency
+ * is not available
*/
-static u8 csiphy_settle_cnt_calc(u32 pixel_clock, u8 bpp, u8 num_lanes,
- u32 timer_clk_rate)
+static u8 csiphy_settle_cnt_calc(s64 link_freq, u32 timer_clk_rate)
{
- u32 mipi_clock; /* Hz */
u32 ui; /* ps */
u32 timer_period; /* ps */
u32 t_hs_prepare_max; /* ps */
u32 t_hs_settle; /* ps */
u8 settle_cnt;

- mipi_clock = pixel_clock * bpp / (2 * num_lanes);
- ui = div_u64(1000000000000LL, mipi_clock);
+ if (link_freq <= 0)
+ return 0;
+
+ ui = div_u64(1000000000000LL, link_freq);
ui /= 2;
t_hs_prepare_max = 85000 + 6 * ui;
t_hs_settle = t_hs_prepare_max;
@@ -137,15 +136,14 @@ static u8 csiphy_settle_cnt_calc(u32 pixel_clock, u8 bpp, u8 num_lanes,

static void csiphy_lanes_enable(struct csiphy_device *csiphy,
struct csiphy_config *cfg,
- u32 pixel_clock, u8 bpp, u8 lane_mask)
+ s64 link_freq, u8 lane_mask)
{
struct csiphy_lanes_cfg *c = &cfg->csi2->lane_cfg;
u8 settle_cnt;
u8 val, l = 0;
int i;

- settle_cnt = csiphy_settle_cnt_calc(pixel_clock, bpp, c->num_data,
- csiphy->timer_clk_rate);
+ settle_cnt = csiphy_settle_cnt_calc(link_freq, csiphy->timer_clk_rate);

val = BIT(c->clk.pos);
for (i = 0; i < c->num_data; i++)
diff --git a/drivers/media/platform/qcom/camss/camss-csiphy.c b/drivers/media/platform/qcom/camss/camss-csiphy.c
index 509c9a59c09c..40384d7ca78c 100644
--- a/drivers/media/platform/qcom/camss/camss-csiphy.c
+++ b/drivers/media/platform/qcom/camss/camss-csiphy.c
@@ -102,23 +102,23 @@ static u8 csiphy_get_bpp(const struct csiphy_format *formats,
static int csiphy_set_clock_rates(struct csiphy_device *csiphy)
{
struct device *dev = csiphy->camss->dev;
- u32 pixel_clock;
+ s64 link_freq;
int i, j;
int ret;

- ret = camss_get_pixel_clock(&csiphy->subdev.entity, &pixel_clock);
- if (ret)
- pixel_clock = 0;
+ u8 bpp = csiphy_get_bpp(csiphy->formats, csiphy->nformats,
+ csiphy->fmt[MSM_CSIPHY_PAD_SINK].code);
+ u8 num_lanes = csiphy->cfg.csi2->lane_cfg.num_data;
+
+ link_freq = camss_get_link_freq(&csiphy->subdev.entity, bpp, num_lanes);
+ if (link_freq < 0)
+ link_freq = 0;

for (i = 0; i < csiphy->nclocks; i++) {
struct camss_clock *clock = &csiphy->clock[i];

if (csiphy->rate_set[i]) {
- u8 bpp = csiphy_get_bpp(csiphy->formats,
- csiphy->nformats,
- csiphy->fmt[MSM_CSIPHY_PAD_SINK].code);
- u8 num_lanes = csiphy->cfg.csi2->lane_cfg.num_data;
- u64 min_rate = pixel_clock * bpp / (2 * num_lanes * 4);
+ u64 min_rate = link_freq / 4;
long round_rate;

camss_add_clock_margin(&min_rate);
@@ -238,22 +238,18 @@ static u8 csiphy_get_lane_mask(struct csiphy_lanes_cfg *lane_cfg)
static int csiphy_stream_on(struct csiphy_device *csiphy)
{
struct csiphy_config *cfg = &csiphy->cfg;
- u32 pixel_clock;
+ s64 link_freq;
u8 lane_mask = csiphy_get_lane_mask(&cfg->csi2->lane_cfg);
u8 bpp = csiphy_get_bpp(csiphy->formats, csiphy->nformats,
csiphy->fmt[MSM_CSIPHY_PAD_SINK].code);
+ u8 num_lanes = csiphy->cfg.csi2->lane_cfg.num_data;
u8 val;
- int ret;

- ret = camss_get_pixel_clock(&csiphy->subdev.entity, &pixel_clock);
- if (ret) {
- dev_err(csiphy->camss->dev,
- "Cannot get CSI2 transmitter's pixel clock\n");
- return -EINVAL;
- }
- if (!pixel_clock) {
+ link_freq = camss_get_link_freq(&csiphy->subdev.entity, bpp, num_lanes);
+
+ if (link_freq < 0) {
dev_err(csiphy->camss->dev,
- "Got pixel clock == 0, cannot continue\n");
+ "Cannot get CSI2 transmitter's link frequency\n");
return -EINVAL;
}

@@ -268,7 +264,7 @@ static int csiphy_stream_on(struct csiphy_device *csiphy)
writel_relaxed(val, csiphy->base_clk_mux);
wmb();

- csiphy->ops->lanes_enable(csiphy, cfg, pixel_clock, bpp, lane_mask);
+ csiphy->ops->lanes_enable(csiphy, cfg, link_freq, lane_mask);

return 0;
}
diff --git a/drivers/media/platform/qcom/camss/camss-csiphy.h b/drivers/media/platform/qcom/camss/camss-csiphy.h
index f7967ef836dc..d71b8bc6ec00 100644
--- a/drivers/media/platform/qcom/camss/camss-csiphy.h
+++ b/drivers/media/platform/qcom/camss/camss-csiphy.h
@@ -50,7 +50,7 @@ struct csiphy_hw_ops {
void (*reset)(struct csiphy_device *csiphy);
void (*lanes_enable)(struct csiphy_device *csiphy,
struct csiphy_config *cfg,
- u32 pixel_clock, u8 bpp, u8 lane_mask);
+ s64 link_freq, u8 lane_mask);
void (*lanes_disable)(struct csiphy_device *csiphy,
struct csiphy_config *cfg);
irqreturn_t (*isr)(int irq, void *dev);
diff --git a/drivers/media/platform/qcom/camss/camss.c b/drivers/media/platform/qcom/camss/camss.c
index 7c0f669f8aa6..eb8fb8c34acd 100644
--- a/drivers/media/platform/qcom/camss/camss.c
+++ b/drivers/media/platform/qcom/camss/camss.c
@@ -548,6 +548,29 @@ struct media_entity *camss_find_sensor(struct media_entity *entity)
}
}

+/**
+ * camss_get_link_freq - Get link frequency from sensor
+ * @entity: Media entity in the current pipeline
+ * @bpp: Number of bits per pixel for the current format
+ * @lanes: Number of lanes in the link to the sensor
+ *
+ * Return link frequency on success or a negative error code otherwise
+ */
+s64 camss_get_link_freq(struct media_entity *entity, unsigned int bpp,
+ unsigned int lanes)
+{
+ struct media_entity *sensor;
+ struct v4l2_subdev *subdev;
+
+ sensor = camss_find_sensor(entity);
+ if (!sensor)
+ return -ENODEV;
+
+ subdev = media_entity_to_v4l2_subdev(sensor);
+
+ return v4l2_get_link_freq(subdev->ctrl_handler, bpp, 2 * lanes);
+}
+
/*
* camss_get_pixel_clock - Get pixel clock rate from sensor
* @entity: Media entity in the current pipeline
diff --git a/drivers/media/platform/qcom/camss/camss.h b/drivers/media/platform/qcom/camss/camss.h
index 3a0484683cd6..86cdc25189eb 100644
--- a/drivers/media/platform/qcom/camss/camss.h
+++ b/drivers/media/platform/qcom/camss/camss.h
@@ -108,6 +108,8 @@ int camss_enable_clocks(int nclocks, struct camss_clock *clock,
struct device *dev);
void camss_disable_clocks(int nclocks, struct camss_clock *clock);
struct media_entity *camss_find_sensor(struct media_entity *entity);
+s64 camss_get_link_freq(struct media_entity *entity, unsigned int bpp,
+ unsigned int lanes);
int camss_get_pixel_clock(struct media_entity *entity, u32 *pixel_clock);
int camss_pm_domain_on(struct camss *camss, int id);
void camss_pm_domain_off(struct camss *camss, int id);
--
2.17.1

Next message: Ahmad Fatoum: "Re: [Linux-stm32] [PATCH v2 12/14] ARM: dts: stm32: move clocks/resets to SCMI resources for stm32mp15"
Previous message: Adrian Hunter: "[PATCH 06/11] perf machine: Factor out machine__idle_thread()"
In reply to: Jacopo Mondi: "Re: [PATCH v2 2/3] media: camss: use v4l2_get_link_freq() to calculate the relevant clocks"
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