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

Andrej Picej
2024-12-12T08:08:14Z

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.

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?

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