Re: [PATCH v5 2/3] drm/bridge: ti-sn65dsi83: Add ti,lvds-vod-swing optional properties

Dmitry Baryshkov
2024-12-12T09:28:10Z

On Thu, Dec 12, 2024 at 09:08:03AM +0100, Andrej Picej wrote:
>
>
> On 12. 12. 24 00:04, Dmitry Baryshkov wrote:
> > On Wed, Dec 11, 2024 at 08:57:17AM +0100, Andrej Picej wrote:
> > >
> > >
> > > On 10. 12. 24 14:59, Dmitry Baryshkov wrote:
> > > > On Tue, Dec 10, 2024 at 02:41:01PM +0100, Andrej Picej wrote:
> > > > >
> > > > >
> > > > > On 10. 12. 24 12:43, Dmitry Baryshkov wrote:
> > > > > > On Tue, Dec 10, 2024 at 10:19:00AM +0100, Andrej Picej wrote:
> > > > > > > Add a optional properties to change LVDS output voltage. This should not
> > > > > > > be static as this depends mainly on the connected display voltage
> > > > > > > requirement. We have three properties:
> > > > > > > - "ti,lvds-termination-ohms", which sets near end termination,
> > > > > > > - "ti,lvds-vod-swing-data-microvolt" and
> > > > > > > - "ti,lvds-vod-swing-clock-microvolt" which both set LVDS differential
> > > > > > > output voltage for data and clock lanes. They are defined as an array
> > > > > > > with min and max values. The appropriate bitfield will be set if
> > > > > > > selected constraints can be met.
> > > > > > >
> > > > > > > If "ti,lvds-termination-ohms" is not defined the default of 200 Ohm near
> > > > > > > end termination will be used. Selecting only one:
> > > > > > > "ti,lvds-vod-swing-data-microvolt" or
> > > > > > > "ti,lvds-vod-swing-clock-microvolt" can be done, but the output voltage
> > > > > > > constraint for only data/clock lanes will be met. Setting both is
> > > > > > > recommended.
> > > > > > >
> > > > > > > Signed-off-by: Andrej Picej <andrej.picej@norik.com>
> > > > > > > ---
> > > > > > > Changes in v5:
> > > > > > > - specify default values in sn65dsi83_parse_lvds_endpoint,
> > > > > > > - move sn65dsi83_parse_lvds_endpoint for channel B up, outside if,
> > > > > > > Changes in v4:
> > > > > > > - fix typo in commit message bitfiled -> bitfield
> > > > > > > - use arrays (lvds_vod_swing_conf and lvds_term_conf) in private data, instead
> > > > > > > of separate variables for channel A/B
> > > > > > > - add more checks on return value of "of_property_read_u32_array"
> > > > > > > Changes in v3:
> > > > > > > - use microvolts for default array values 1000 mV -> 1000000 uV.
> > > > > > > Changes in v2:
> > > > > > > - use datasheet tables to get the proper configuration
> > > > > > > - since major change was done change the authorship to myself
> > > > > > > ---
> > > > > > > drivers/gpu/drm/bridge/ti-sn65dsi83.c | 142 +++++++++++++++++++++++++-
> > > > > > > 1 file changed, 139 insertions(+), 3 deletions(-)
> > > > > > >
> > > > > > > diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi83.c b/drivers/gpu/drm/bridge/ti-sn65dsi83.c
> > > > > > > index 57a7ed13f996..f9578b38da28 100644
> > > > > > > --- a/drivers/gpu/drm/bridge/ti-sn65dsi83.c
> > > > > > > +++ b/drivers/gpu/drm/bridge/ti-sn65dsi83.c
> > > > > > > @@ -132,6 +132,16 @@
> > > > > > > #define REG_IRQ_STAT_CHA_SOT_BIT_ERR BIT(2)
> > > > > > > #define REG_IRQ_STAT_CHA_PLL_UNLOCK BIT(0)
> > > > > > > +enum sn65dsi83_channel {
> > > > > > > + CHANNEL_A,
> > > > > > > + CHANNEL_B
> > > > > > > +};
> > > > > > > +
> > > > > > > +enum sn65dsi83_lvds_term {
> > > > > > > + OHM_100,
> > > > > > > + OHM_200
> > > > > > > +};
> > > > > > > +
> > > > > > > enum sn65dsi83_model {
> > > > > > > MODEL_SN65DSI83,
> > > > > > > MODEL_SN65DSI84,
> > > > > > > @@ -147,6 +157,8 @@ struct sn65dsi83 {
> > > > > > > struct regulator *vcc;
> > > > > > > bool lvds_dual_link;
> > > > > > > bool lvds_dual_link_even_odd_swap;
> > > > > > > + int lvds_vod_swing_conf[2];
> > > > > > > + int lvds_term_conf[2];
> > > > > > > };
> > > > > > > static const struct regmap_range sn65dsi83_readable_ranges[] = {
> > > > > > > @@ -237,6 +249,36 @@ static const struct regmap_config sn65dsi83_regmap_config = {
> > > > > > > .max_register = REG_IRQ_STAT,
> > > > > > > };
> > > > > > > +static const int lvds_vod_swing_data_table[2][4][2] = {
> > > > > > > + { /* 100 Ohm */
> > > > > > > + { 180000, 313000 },
> > > > > > > + { 215000, 372000 },
> > > > > > > + { 250000, 430000 },
> > > > > > > + { 290000, 488000 },
> > > > > > > + },
> > > > > > > + { /* 200 Ohm */
> > > > > > > + { 150000, 261000 },
> > > > > > > + { 200000, 346000 },
> > > > > > > + { 250000, 428000 },
> > > > > > > + { 300000, 511000 },
> > > > > > > + },
> > > > > > > +};
> > > > > > > +
> > > > > > > +static const int lvds_vod_swing_clock_table[2][4][2] = {
> > > > > > > + { /* 100 Ohm */
> > > > > > > + { 140000, 244000 },
> > > > > > > + { 168000, 290000 },
> > > > > > > + { 195000, 335000 },
> > > > > > > + { 226000, 381000 },
> > > > > > > + },
> > > > > > > + { /* 200 Ohm */
> > > > > > > + { 117000, 204000 },
> > > > > > > + { 156000, 270000 },
> > > > > > > + { 195000, 334000 },
> > > > > > > + { 234000, 399000 },
> > > > > > > + },
> > > > > > > +};
> > > > > > > +
> > > > > > > static struct sn65dsi83 *bridge_to_sn65dsi83(struct drm_bridge *bridge)
> > > > > > > {
> > > > > > > return container_of(bridge, struct sn65dsi83, bridge);
> > > > > > > @@ -435,12 +477,16 @@ static void sn65dsi83_atomic_pre_enable(struct drm_bridge *bridge,
> > > > > > > val |= REG_LVDS_FMT_LVDS_LINK_CFG;
> > > > > > > regmap_write(ctx->regmap, REG_LVDS_FMT, val);
> > > > > > > - regmap_write(ctx->regmap, REG_LVDS_VCOM, 0x05);
> > > > > > > + regmap_write(ctx->regmap, REG_LVDS_VCOM,
> > > > > > > + REG_LVDS_VCOM_CHA_LVDS_VOD_SWING(ctx->lvds_vod_swing_conf[CHANNEL_A]) |
> > > > > > > + REG_LVDS_VCOM_CHB_LVDS_VOD_SWING(ctx->lvds_vod_swing_conf[CHANNEL_B]));
> > > > > > > regmap_write(ctx->regmap, REG_LVDS_LANE,
> > > > > > > (ctx->lvds_dual_link_even_odd_swap ?
> > > > > > > REG_LVDS_LANE_EVEN_ODD_SWAP : 0) |
> > > > > > > - REG_LVDS_LANE_CHA_LVDS_TERM |
> > > > > > > - REG_LVDS_LANE_CHB_LVDS_TERM);
> > > > > > > + (ctx->lvds_term_conf[CHANNEL_A] ?
> > > > > > > + REG_LVDS_LANE_CHA_LVDS_TERM : 0) |
> > > > > > > + (ctx->lvds_term_conf[CHANNEL_B] ?
> > > > > > > + REG_LVDS_LANE_CHB_LVDS_TERM : 0));
> > > > > > > regmap_write(ctx->regmap, REG_LVDS_CM, 0x00);
> > > > > > > le16val = cpu_to_le16(mode->hdisplay);
> > > > > > > @@ -576,10 +622,100 @@ static const struct drm_bridge_funcs sn65dsi83_funcs = {
> > > > > > > .atomic_get_input_bus_fmts = sn65dsi83_atomic_get_input_bus_fmts,
> > > > > > > };
> > > > > > > +static int sn65dsi83_select_lvds_vod_swing(struct device *dev,
> > > > > > > + u32 lvds_vod_swing_data[2], u32 lvds_vod_swing_clk[2], u8 lvds_term)
> > > > > > > +{
> > > > > > > + int i;
> > > > > > > +
> > > > > > > + for (i = 0; i <= 3; i++) {
> > > > > > > + if (lvds_vod_swing_data_table[lvds_term][i][0] >= lvds_vod_swing_data[0] &&
> > > > > > > + lvds_vod_swing_data_table[lvds_term][i][1] <= lvds_vod_swing_data[1] &&
> > > > > > > + lvds_vod_swing_clock_table[lvds_term][i][0] >= lvds_vod_swing_clk[0] &&
> > > > > > > + lvds_vod_swing_clock_table[lvds_term][i][1] <= lvds_vod_swing_clk[1])
> > > > > > > + return i;
> > > > > > > + }
> > > > > > > +
> > > > > > > + dev_err(dev, "failed to find appropriate LVDS_VOD_SWING configuration\n");
> > > > > > > + return -EINVAL;
> > > > > > > +}
> > > > > > > +
> > > > > > > +static int sn65dsi83_parse_lvds_endpoint(struct sn65dsi83 *ctx, int channel)
> > > > > > > +{
> > > > > > > + struct device *dev = ctx->dev;
> > > > > > > + struct device_node *endpoint;
> > > > > > > + int endpoint_reg;
> > > > > > > + /* Set so the property can be freely selected if not defined */
> > > > > > > + u32 lvds_vod_swing_data[2] = { 0, 1000000 };
> > > > > > > + u32 lvds_vod_swing_clk[2] = { 0, 1000000 };
> > > > > > > + u32 lvds_term;
> > > > > > > + u8 lvds_term_conf = 0x1;
> > > > > > > + int lvds_vod_swing_conf = 0x1;
> > > > > >
> > > > > > Magic values
> > > > >
> > > > > Can you please elaborate.
> > > > >
> > > > > I can use:
> > > > > u8 lvds_term_conf = OHM_200;
> > > > >
> > > > > What about lvds_vod_swing_conf? Should I create additional define for it?
> > > > > But this doesn't solve a hidden meaning? Maybe additional comment above?
> > > > > Would like to avoid using voltages for it, since then we are reverse
> > > > > engineering the table in datasheet to match the default reg value.
> > > >
> > > > I think the following example solves both problems:
> > > >
> > > > lvds_term = 200;
> > > > of_property_read_u32(..., &lvds_term);
> > > >
> > > > if (lvds_term == 100)
> > > > ctx->lvds_term_conf[channel] = OHM_100;
> > > > else if (lvds_term == 200)
> > > > ctx->lvds_term_conf[channel] = OHM_200;
> > > > else
> > > > return -EINVAL;
> > > >
> > > > The same approach can be applied to lvds_vod_swing_conf, resulting in
> > > > removal of magic values.
> > >
> > > Sorry, but I think it is not that easy when it comes to the
> > > lvds_vod_swing_conf. We should assign default value if
> > > "ti,lvds-vod-swing-data-microvolt" and "ti,lvds-vod-swing-clock-microvolt"
> > > are not defined. Default value of the lvds_vod_swing_conf is 0x1, but this
> > > doesn't have any straight forward meaning like OHM_200 for example.
> > >
> > > What we can do in that case is that we copy the values from defined
> > > datasheet tables to the "lvds_vod_swing_data[2]" and "lvds_vod_swing_clk[2]"
> > > arrays and then run the
> > > sn65dsi83_select_lvds_vod_swing with it, which will return the default value
> > > (0x1).
> > >
> > > /* If both properties are not defined assign default limits */
> > > if (ret_data && ret_clock) {
> > > memcpy(lvds_vod_swing_data,
> > > lvds_vod_swing_data_table[ctx->lvds_term_conf[channel]][1],
> > > sizeof(lvds_vod_swing_data));
> > > memcpy(lvds_vod_swing_clk,
> > > lvds_vod_swing_clock_table[ctx->lvds_term_conf[channel]][1],
> > > sizeof(lvds_vod_swing_clk));
> > > }
> > > lvds_vod_swing_conf = sn65dsi83_select_lvds_vod_swing(dev,
> > > lvds_vod_swing_data, lvds_vod_swing_clk,
> > > ctx->lvds_term_conf[channel]);
> > > if (lvds_vod_swing_conf < 0) {
> > > ret = lvds_vod_swing_conf;
> > > goto exit;
> > > }
> > >
> > > ctx->lvds_vod_swing_conf[channel] = lvds_vod_swing_conf;
> > >
> > > I'm not sure if using this approach gets rid of the problem with magic
> > > values.
> > > Or maybe I'm not seeing the obvious solution so please bear with me.
> >
> > Yes, the defaults (0..1000000) should be fixed to result in the same
> > value (0x01) as if the property wasn't specified at all
>
> The defaults (0..1000000) is selected because in case if only one property
> is defined in dts (ti,lvds-vod-swing-data-microvolt or
> ti,lvds-vod-swing-clock-microvolt) the other array values don't effect the
> decision which "lvds_vod_swing_conf" is selected. That's why we initialized
> the array to be out off bounds of the datasheet tables, all values in the
> table match the not defined property, so lvds_vod_swing_conf is selected
> purely on the basis of the defined property.

I see, thanks for the explanation.

>
> Example:
> DTS
> ti,lvds-vod-swing-data-microvolt = <250000 428000>;
> //ti,lvds-vod-swing-clock-microvolt NOT DEFINED;
>
> After parsing the devicetree we will get:
> lvds_vod_swing_data = [ 250000, 428000 ]
> lvds_vod_swing_clk = [ 0, 1000000 ]
>
> In sn65dsi83_select_lvds_vod_swing lvds_vod_swing_clk[] values don't effect
> the decision making since
>
> lvds_vod_swing_clock_table[lvds_term][i][0] >= lvds_vod_swing_clk[0] &&
> lvds_vod_swing_clock_table[lvds_term][i][1] <= lvds_vod_swing_clk[1]
>
> is always true.
>
> >
> > I think the following should work:
> >
> > /* artifical values to select the defaults in both cases */
> > u32 lvds_vod_swing_data[2] = { 190000, 330000 };
> > u32 lvds_vod_swing_clk[2] = { 150000, 250000 };
>
> This sets the default to 0x0. It should be:
> u32 lvds_vod_swing_data[2] = { 200000, 372000 };
> u32 lvds_vod_swing_clk[2] = { 156000, 290000 };
> This selects the default 0x1 in both cases, if termination is 100 or 200
> Ohms.
>
> Nevertheless I think I got your point. But I would still like to give the
> user the freedom to only specify one property if maybe connected panel only
> has limits on data lanes/clock lane.
> So maybe set the arrays lvds_vod_swing_data/clk to [0, 1000000] if
> of_property_read_u32_array returns -EINVAL (property does not exist).
> What do you say?

After your explanation, I think it might be better to explicitly set the
value to 0x1, but not at the top of the function, but next to a check
that both properties are (not) set.

>
> >
> > Yes, they are artificial, as stated in the comment. Yes, I think it's
> > better than special-casing in the property handling.
> >

--
With best wishes
Dmitry