Re: [PATCH v6 2/5] media: hi846: Fix link frequency handling

[Pengyu Luo]

On Wed, Sep 2, 2026 at 5:24 PM Sakari Ailus
<sakari.ailus@xxxxxxxxxxxxxxx> wrote:
>
> Hi Pengyu,
>
> Thanks for the update.
>

I am glad to see your review too!

> On Mon, Aug 31, 2026 at 12:00:22AM +0800, Pengyu Luo wrote:
> > Link frequency is tied to PLL configuration, lane count, and external
> > and configurable clock, so use runtime here instead of hardcoding for
> > specific configuration. To implement this, we do
> >
> > 1. Drop fixed link freqs, we calculate the driver supported values and
> > use v4l2_link_freq_to_bitmap() to get the intersection with the DT
> > supported values.
> >
> > 2. Attach mipi_clk_div_{2,4}lane to current mode, and use the div with
> > mclk clock, lane count to calculate link frequency.
> >
> > 3. Drop mclk clock rate check.
> >
> > Fixes: e8c0882685f9 ("media: i2c: add driver for the SK Hynix Hi-846 8M pixel camera")
> > Signed-off-by: Pengyu Luo <mitltlatltl@xxxxxxxxx>
> > ---
> > v6:
> > - Add link freq ctrl back (Sakari)
> > - Use v4l2_link_freq_to_bitmap() to get matched link freqs (Sakari)
> > - Move clk_get() before than hi846_parse_dt(), since we use clock in hi846_parse_dt()
> > v5:
> > - Use separated fields instead of raw register values for PLL cfg (Sakari)
> > - Use mul_u64_u32_div() to avoid loss of pricision and u64/u32 issues (Sakari)
> > - Drop line break (Sakari)
> > ---
> >  drivers/media/i2c/hi846.c | 151 ++++++++++++++++++++++++--------------
> >  1 file changed, 94 insertions(+), 57 deletions(-)
> >
> > diff --git a/drivers/media/i2c/hi846.c b/drivers/media/i2c/hi846.c
> > index 7f069aca0fce..2f8624f9bdf3 100644
> > --- a/drivers/media/i2c/hi846.c
> > +++ b/drivers/media/i2c/hi846.c
> > @@ -1,7 +1,7 @@
> >  // SPDX-License-Identifier: GPL-2.0
> >  // Copyright (c) 2021 Purism SPC
> >
> > -#include <linux/unaligned.h>
> > +#include <linux/bitfield.h>
> >  #include <linux/clk.h>
> >  #include <linux/delay.h>
> >  #include <linux/gpio/consumer.h>
> > @@ -11,6 +11,7 @@
> >  #include <linux/pm.h>
> >  #include <linux/property.h>
> >  #include <linux/regulator/consumer.h>
> > +#include <linux/unaligned.h>
> >  #include <media/v4l2-ctrls.h>
> >  #include <media/v4l2-device.h>
> >  #include <media/v4l2-fwnode.h>
> > @@ -219,8 +220,8 @@ struct hi846_mode {
> >       /* Horizontal timing size */
> >       u32 llp;
> >
> > -     /* Link frequency needed for this resolution */
> > -     u8 link_freq_index;
> > +     u8 mipi_clk_div_2lane;
> > +     u8 mipi_clk_div_4lane;
> >
> >       u16 fps;
> >
> > @@ -1040,13 +1041,6 @@ static const char * const hi846_test_pattern_menu[] = {
> >       "Resolution Pattern",
> >  };
> >
> > -#define FREQ_INDEX_640       0
> > -#define FREQ_INDEX_1280      1
> > -static const s64 hi846_link_freqs[] = {
> > -     [FREQ_INDEX_640] = 80000000,
> > -     [FREQ_INDEX_1280] = 200000000,
> > -};
> > -
> >  static const struct hi846_reg_list hi846_init_regs_list_2lane = {
> >       .num_of_regs = ARRAY_SIZE(hi846_init_2lane),
> >       .regs = hi846_init_2lane,
> > @@ -1061,7 +1055,13 @@ static const struct hi846_mode supported_modes[] = {
> >       {
> >               .width = 640,
> >               .height = 480,
> > -             .link_freq_index = FREQ_INDEX_640,
> > +             .mipi_clk_div_2lane = 4,
> > +             /*
> > +              * Dummy but necessary if we set this mode default, otherwise
> > +              * hi846_calc_pixel_rate() will be broken in
> > +              * hi846_init_controls()
> > +              */
> > +             .mipi_clk_div_4lane = 8,
>
> The divider of the 4-lane case appears to be always two times that of the
> 2-lane case. Could you calculate the value instead?
>

Ack

> I think it'd be better to keep the link frequencies and modes at separate
> indices; this is the way it used to be, too.
>

You mean add an array for the divider ratios then use the indices in
modes like before?

> >               .fps = 120,
> >               .frame_len = 631,
> >               .llp = HI846_LINE_LENGTH,
> > @@ -1086,7 +1086,8 @@ static const struct hi846_mode supported_modes[] = {
> >       {
> >               .width = 1280,
> >               .height = 720,
> > -             .link_freq_index = FREQ_INDEX_1280,
> > +             .mipi_clk_div_2lane = 2,
> > +             .mipi_clk_div_4lane = 4,
> >               .fps = 90,
> >               .frame_len = 842,
> >               .llp = HI846_LINE_LENGTH,
> > @@ -1112,7 +1113,8 @@ static const struct hi846_mode supported_modes[] = {
> >       {
> >               .width = 1632,
> >               .height = 1224,
> > -             .link_freq_index = FREQ_INDEX_1280,
> > +             .mipi_clk_div_2lane = 2,
> > +             .mipi_clk_div_4lane = 4,
> >               .fps = 30,
> >               .frame_len = 2526,
> >               .llp = HI846_LINE_LENGTH,
> > @@ -1167,6 +1169,9 @@ struct hi846 {
> >       struct v4l2_ctrl *hblank;
> >       struct v4l2_ctrl *exposure;
> >
> > +     s64 link_freqs[ARRAY_SIZE(supported_modes)];
> > +     int num_link_freqs;
> > +
> >       struct mutex mutex; /* protect cur_mode, streaming and chip access */
> >       const struct hi846_mode *cur_mode;
> >       bool streaming;
> > @@ -1192,21 +1197,41 @@ static const struct hi846_datafmt *hi846_find_datafmt(u32 code)
> >       return NULL;
> >  }
> >
> > -static inline u8 hi846_get_link_freq_index(struct hi846 *hi846)
> > +static u64
> > +hi846_get_link_freq(const struct hi846 *hi846, const struct hi846_mode *mode)
> >  {
> > -     return hi846->cur_mode->link_freq_index;
> > +     u64 mclk = clk_get_rate(hi846->clock);
> > +     u8 mipi_clk_div;
> > +
> > +     if (hi846->nr_lanes == 2)
> > +             mipi_clk_div = mode->mipi_clk_div_2lane;
> > +     else
> > +             mipi_clk_div = mode->mipi_clk_div_4lane;
> > +
> > +     /*
> > +      * HI846_REG_PLL_CFG_MIPI1_H = 0x025a, it is fixed in listed modes
> > +      * [11:8]: 0x02 => pre_div = 3
> > +      * [7:0]: 0x5a => multiplier = 90
> > +      */
> > +     return mul_u64_u32_div(mclk, 90, 3 * mipi_clk_div);
> >  }
> >
> > -static u64 hi846_get_link_freq(struct hi846 *hi846)
> > +static int hi846_get_link_freq_index(const struct hi846 *hi846,
> > +                                  const struct hi846_mode *mode)
> >  {
> > -     u8 index = hi846_get_link_freq_index(hi846);
> > +     u64 link_freq = hi846_get_link_freq(hi846, mode);
> > +     int i;
> > +
> > +     for (i = 0; i < hi846->num_link_freqs; i++)
> > +             if (hi846->link_freqs[i] == link_freq)
> > +                     return i;
> >
> > -     return hi846_link_freqs[index];
> > +     return -EINVAL;
> >  }
> >
> >  static u64 hi846_calc_pixel_rate(struct hi846 *hi846)
> >  {
> > -     u64 link_freq = hi846_get_link_freq(hi846);
> > +     u64 link_freq = hi846_get_link_freq(hi846, hi846->cur_mode);
> >       u64 pixel_rate = link_freq * 2 * hi846->nr_lanes;
> >
> >       do_div(pixel_rate, HI846_RGB_DEPTH);
> > @@ -1429,8 +1454,8 @@ static int hi846_init_controls(struct hi846 *hi846)
> >       hi846->link_freq =
> >               v4l2_ctrl_new_int_menu(ctrl_hdlr, &hi846_ctrl_ops,
> >                                      V4L2_CID_LINK_FREQ,
> > -                                    ARRAY_SIZE(hi846_link_freqs) - 1,
> > -                                    0, hi846_link_freqs);
> > +                                    hi846->num_link_freqs - 1,
> > +                                    0, hi846->link_freqs);
> >       if (hi846->link_freq)
> >               hi846->link_freq->flags |= V4L2_CTRL_FLAG_READ_ONLY;
> >
> > @@ -1503,10 +1528,9 @@ static int hi846_set_video_mode(struct hi846 *hi846, int fps)
> >       u64 frame_length;
> >       int ret = 0;
> >       int dummy_lines;
> > -     u64 link_freq = hi846_get_link_freq(hi846);
> > +     u64 link_freq = hi846_get_link_freq(hi846, hi846->cur_mode);
> >
> > -     dev_dbg(&client->dev, "%s: link freq: %llu\n", __func__,
> > -             hi846_get_link_freq(hi846));
> > +     dev_dbg(&client->dev, "%s: link freq: %llu\n", __func__, link_freq);
> >
> >       do_div(link_freq, fps);
> >       frame_length = link_freq;
> > @@ -1699,6 +1723,7 @@ static int hi846_set_format(struct v4l2_subdev *sd,
> >       const struct hi846_datafmt *fmt = hi846_find_datafmt(mf->code);
> >       u32 tgt_fps;
> >       s32 vblank_def, h_blank;
> > +     int idx;
> >
> >       if (!fmt) {
> >               mf->code = hi846_colour_fmts[0].code;
> > @@ -1749,7 +1774,14 @@ static int hi846_set_format(struct v4l2_subdev *sd,
> >       mf->code = HI846_MEDIA_BUS_FORMAT;
> >       mf->field = V4L2_FIELD_NONE;
> >
> > -     __v4l2_ctrl_s_ctrl(hi846->link_freq, hi846_get_link_freq_index(hi846));
> > +     idx = hi846_get_link_freq_index(hi846, hi846->cur_mode);
> > +     if (idx < 0) {
> > +             dev_err(&client->dev,
> > +                     "failed to get link freq index: %d\n", idx);
> > +             return -EINVAL;
> > +     }
> > +
> > +     __v4l2_ctrl_s_ctrl(hi846->link_freq, idx);
> >       __v4l2_ctrl_s_ctrl_int64(hi846->pixel_rate,
> >                                hi846_calc_pixel_rate(hi846));
> >
> > @@ -1947,20 +1979,33 @@ static int hi846_identify_module(struct hi846 *hi846)
> >       return 0;
> >  }
> >
> > -static s64 hi846_check_link_freqs(struct hi846 *hi846,
> > -                               struct v4l2_fwnode_endpoint *ep)
> > +static int hi846_add_link_freqs(struct hi846 *hi846, struct device *dev,
> > +                             struct v4l2_fwnode_endpoint *ep)
> >  {
> > -     const s64 *freqs = hi846_link_freqs;
> > -     int freqs_count = ARRAY_SIZE(hi846_link_freqs);
> > -     int i, j;
> > -
> > -     for (i = 0; i < freqs_count; i++) {
> > -             for (j = 0; j < ep->nr_of_link_frequencies; j++)
> > -                     if (freqs[i] == ep->link_frequencies[j])
> > -                             break;
> > -             if (j == ep->nr_of_link_frequencies)
> > -                     return freqs[i];
> > -     }
> > +     s64 hi846_link_freqs[ARRAY_SIZE(supported_modes)];
> > +     unsigned long freq_bitmap;
> > +     int ret, i;
> > +
> > +     /*
> > +      * Since the MCLK freq varies between platforms, calculating driver
> > +      * supported link freqs here.
> > +      */
> > +     for (i = 0; i < ARRAY_SIZE(supported_modes); i++)
> > +             hi846_link_freqs[i] = hi846_get_link_freq(hi846, &supported_modes[i]);
> > +
> > +     ret = v4l2_link_freq_to_bitmap(dev, ep->link_frequencies,
> > +                                    ep->nr_of_link_frequencies,
> > +                                    hi846_link_freqs,
> > +                                    ARRAY_SIZE(hi846_link_freqs),
> > +                                    &freq_bitmap);
> > +     if (ret || !freq_bitmap)
> > +             return ret;
> > +
> > +     for (i = 0; i < ARRAY_SIZE(hi846_link_freqs); i++)
>
> Could you use the hi846_link_freqs array as-is for the control?
>

Could you please tell me if an array with repeat numbers is acceptable
for v4l2_ctrl_new_int_menu(), if so, keep it as-is is more convenient
later.

> The selectable modes are expected to depend on the chose link frequency,
> which is not affected by setting the format, for instance. I wonder if it'd
> be useful to squash the next patch into this one.
>

Yes, it seems so, we need to get the index of link freq to set
control, so we can filter the mode by the index, and this lets us drop
previous checks.

Best wishes,
Pengyu


> > +             if (BIT(i) & freq_bitmap) {
> > +                     hi846->link_freqs[hi846->num_link_freqs++] = hi846_link_freqs[i];
> > +                     dev_dbg(dev, "Add supported link frequency %lld\n", hi846_link_freqs[i]);
> > +             }
> >
> >       return 0;
> >  }
> > @@ -1973,7 +2018,6 @@ static int hi846_parse_dt(struct hi846 *hi846, struct device *dev)
> >               .bus_type = V4L2_MBUS_CSI2_DPHY
> >       };
> >       int ret;
> > -     s64 fq;
> >
> >       ep = fwnode_graph_get_next_endpoint(fwnode, NULL);
> >       if (!ep) {
> > @@ -2004,11 +2048,10 @@ static int hi846_parse_dt(struct hi846 *hi846, struct device *dev)
> >               goto check_hwcfg_error;
> >       }
> >
> > -     /* Check that link frequences for all the modes are in device tree */
> > -     fq = hi846_check_link_freqs(hi846, &bus_cfg);
> > -     if (fq) {
> > -             dev_err(dev, "Link frequency of %lld is not supported\n", fq);
> > -             ret = -EINVAL;
> > +     /* Add link frequencies which are supported by both DT and the driver */
> > +     ret = hi846_add_link_freqs(hi846, dev, &bus_cfg);
> > +     if (ret) {
> > +             dev_err(dev, "failed to add link frequency %d\n", ret);
> >               goto check_hwcfg_error;
> >       }
> >
> > @@ -2041,30 +2084,24 @@ static int hi846_probe(struct i2c_client *client)
> >       struct hi846 *hi846;
> >       int ret;
> >       int i;
> > -     u32 mclk_freq;
> >
> >       hi846 = devm_kzalloc(&client->dev, sizeof(*hi846), GFP_KERNEL);
> >       if (!hi846)
> >               return -ENOMEM;
> >
> > -     ret = hi846_parse_dt(hi846, &client->dev);
> > -     if (ret) {
> > -             dev_err(&client->dev, "failed to check HW configuration: %d",
> > -                     ret);
> > -             return ret;
> > -     }
> > -
> > +     /* Get the MCLK first, since we need it to calculate link freqs */
> >       hi846->clock = devm_v4l2_sensor_clk_get(&client->dev, NULL);
> >       if (IS_ERR(hi846->clock))
> >               return dev_err_probe(&client->dev, PTR_ERR(hi846->clock),
> >                                    "failed to get clock: %pe\n",
> >                                    hi846->clock);
> >
> > -     mclk_freq = clk_get_rate(hi846->clock);
> > -     if (mclk_freq != 25000000)
> > -             dev_warn(&client->dev,
> > -                      "External clock freq should be 25000000, not %u.\n",
> > -                      mclk_freq);
> > +     ret = hi846_parse_dt(hi846, &client->dev);
> > +     if (ret) {
> > +             dev_err(&client->dev, "failed to check HW configuration: %d",
> > +                     ret);
> > +             return ret;
> > +     }
> >
> >       for (i = 0; i < HI846_NUM_SUPPLIES; i++)
> >               hi846->supplies[i].supply = hi846_supply_names[i];
>
> --
> Regards,
>
> Sakari Ailus