Hi Doug, On Tue, May 05, 2020 at 10:59:30AM -0700, Doug Anderson wrote: > On Tue, May 5, 2020 at 1:24 AM Laurent Pinchart wrote: > > On Mon, May 04, 2020 at 09:36:31PM -0700, Douglas Anderson wrote: > > > The ti-sn65dsi86 MIPI DSI to eDP bridge chip supports arbitrary > > > remapping of eDP lanes and also polarity inversion. Both of these > > > features have been described in the device tree bindings for the > > > device since the beginning but were never implemented in the driver. > > > Implement both of them. > > > > > > Part of this change also allows you to (via the same device tree > > > bindings) specify to use fewer than the max number of DP lanes that > > > the panel reports. This could be useful if your display supports more > > > lanes but only a few are hooked up on your board. > > > > > > Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx> > > > --- > > > This patch is based upon my my outstanding series[1] not because there > > > is any real requirement but simply to avoid merge conflicts. I > > > believe that my previous series is ready to land. If, however, you'd > > > prefer that I rebase this patch somewhere atop something else then > > > please shout. > > > > > > [1] https://lore.kernel.org/r/20200430194617.197510-1-dianders@xxxxxxxxxxxx > > > > > > drivers/gpu/drm/bridge/ti-sn65dsi86.c | 75 ++++++++++++++++++++++----- > > > 1 file changed, 62 insertions(+), 13 deletions(-) > > > > > > diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c > > > index 1a125423eb07..52cca54b525f 100644 > > > --- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c > > > +++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c > > > @@ -50,8 +50,12 @@ > > > #define SN_CHA_VERTICAL_BACK_PORCH_REG 0x36 > > > #define SN_CHA_HORIZONTAL_FRONT_PORCH_REG 0x38 > > > #define SN_CHA_VERTICAL_FRONT_PORCH_REG 0x3A > > > +#define SN_LN_ASSIGN_REG 0x59 > > > +#define LN_ASSIGN_WIDTH 2 > > > #define SN_ENH_FRAME_REG 0x5A > > > #define VSTREAM_ENABLE BIT(3) > > > +#define LN_POLRS_OFFSET 4 > > > +#define LN_POLRS_MASK 0xf0 > > > #define SN_DATA_FORMAT_REG 0x5B > > > #define BPP_18_RGB BIT(0) > > > #define SN_HPD_DISABLE_REG 0x5C > > > @@ -98,6 +102,7 @@ > > > > > > #define SN_REGULATOR_SUPPLY_NUM 4 > > > > > > +#define SN_MAX_DP_LANES 4 > > > #define SN_NUM_GPIOS 4 > > > > > > /** > > > @@ -115,6 +120,8 @@ > > > * @enable_gpio: The GPIO we toggle to enable the bridge. > > > * @supplies: Data for bulk enabling/disabling our regulators. > > > * @dp_lanes: Count of dp_lanes we're using. > > > + * @ln_assign: Value to program to the LN_ASSIGN register. > > > + * @ln_polr: Value for the 4-bit LN_POLRS field of SN_ENH_FRAME_REG. > > > * > > > * @gchip: If we expose our GPIOs, this is used. > > > * @gchip_output: A cache of whether we've set GPIOs to output. This > > > @@ -140,6 +147,8 @@ struct ti_sn_bridge { > > > struct gpio_desc *enable_gpio; > > > struct regulator_bulk_data supplies[SN_REGULATOR_SUPPLY_NUM]; > > > int dp_lanes; > > > + u8 ln_assign; > > > + u8 ln_polrs; > > > > > > struct gpio_chip gchip; > > > DECLARE_BITMAP(gchip_output, SN_NUM_GPIOS); > > > @@ -707,26 +716,20 @@ static void ti_sn_bridge_enable(struct drm_bridge *bridge) > > > int dp_rate_idx; > > > unsigned int val; > > > int ret = -EINVAL; > > > + int max_dp_lanes; > > > > > > - /* > > > - * Run with the maximum number of lanes that the DP sink supports. > > > - * > > > - * Depending use cases, we might want to revisit this later because: > > > - * - It's plausible that someone may have run fewer lines to the > > > - * sink than the sink actually supports, assuming that the lines > > > - * will just be driven at a higher rate. > > > - * - The DP spec seems to indicate that it's more important to minimize > > > - * the number of lanes than the link rate. > > > - * > > > - * If we do revisit, it would be important to measure the power impact. > > > - */ > > > - pdata->dp_lanes = ti_sn_get_max_lanes(pdata); > > > + max_dp_lanes = ti_sn_get_max_lanes(pdata); > > > + pdata->dp_lanes = min(pdata->dp_lanes, max_dp_lanes); > > > > > > /* DSI_A lane config */ > > > val = CHA_DSI_LANES(4 - pdata->dsi->lanes); > > > regmap_update_bits(pdata->regmap, SN_DSI_LANES_REG, > > > CHA_DSI_LANES_MASK, val); > > > > > > + regmap_write(pdata->regmap, SN_LN_ASSIGN_REG, pdata->ln_assign); > > > + regmap_update_bits(pdata->regmap, SN_ENH_FRAME_REG, LN_POLRS_MASK, > > > + pdata->ln_polrs << LN_POLRS_OFFSET); > > > + > > > /* set dsi clk frequency value */ > > > ti_sn_bridge_set_dsi_rate(pdata); > > > > > > @@ -1063,6 +1066,50 @@ static int ti_sn_setup_gpio_controller(struct ti_sn_bridge *pdata) > > > return ret; > > > } > > > > > > +static void ti_sn_bridge_parse_lanes(struct ti_sn_bridge *pdata, > > > + struct device_node *np) > > > +{ > > > + u32 lane_assignments[SN_MAX_DP_LANES] = { 0, 1, 2, 3 }; > > > + u32 lane_polarities[SN_MAX_DP_LANES] = { }; > > > + struct device_node *endpoint; > > > + u8 ln_assign = 0; > > > + u8 ln_polrs = 0; > > > + int dp_lanes; > > > + int i; > > > + > > > + /* > > > + * Read config from the device tree about lane remapping and lane > > > + * polarities. These are optional and we assume identity map and > > > + * normal polarity if nothing is specified. It's OK to specify just > > > + * data-lanes but not lane-polarities but not vice versa. > > > + */ > > > + endpoint = of_graph_get_endpoint_by_regs(np, 1, -1); > > > > Shouldn't you check for endpoint == NULL and fail probe if it is ? > > I will if you feel strongly, but I don't think it's necessary. Specifically: > > 1. By design of_property_count_u32_elems() will return an error if > passed a NULL node pointer. > > 2. When we see an error this function will just init things to defaults. > > 3. Later code which really needs the endpoint to hook things up > properly will catch the error and yell. > > ...so while I could add a yell here it doesn't seem like it gains much. As long as it doesn't crash and we eventually catch the error I'm fine. I usually try to catch them early as otherwise it gets harder to make sure all code paths are sanitized. Up to you. > > > + dp_lanes = of_property_count_u32_elems(endpoint, "data-lanes"); > > > + if (dp_lanes > 0) { > > > + of_property_read_u32_array(endpoint, "data-lanes", > > > + lane_assignments, dp_lanes); > > > + of_property_read_u32_array(endpoint, "lane-polarities", > > > + lane_polarities, dp_lanes); > > > > Similarly, with a buggy DT, you may have a buffer overrun here. I would > > first check that dp_lanes <= SN_MAX_DP_LANES and error out otherwise. > > I will definitely add that. Buffer overrun is no bueno. > > > > + } else { > > > + dp_lanes = SN_MAX_DP_LANES; > > > + } > > > + > > > + /* > > > + * Convert into register format. Loop over all lanes even if > > > + * data-lanes had fewer elements so that we nicely initialize > > > + * the LN_ASSIGN register. > > > + */ > > > + for (i = SN_MAX_DP_LANES - 1; i >= 0; i--) { > > > + ln_assign = ln_assign << LN_ASSIGN_WIDTH | lane_assignments[i]; > > > + ln_polrs = ln_polrs << 1 | lane_polarities[i]; > > > + } > > > > The datasheet documents the lane remapping register as allowing pretty > > much any combination, but "Table 12. Logical to Physical Supported > > Combinations" only documents a subset (for instance data-lanes = <2 3> > > isn't allowed in that table). Should we guard against invalid > > configurations ? > > As I understand it, in general standard kernel policy is to not sanity > check the DT _too_ much. This feels a bit on the border. It's up to > the person designing the board and writing the dts to not get things > like this wrong just like it's up to them to make sure they've setup > the i2c pins for our bus w/ the right pullups, configured our > interrupt properly, not overvolted things, put in the correct address > for MMIO, etc. > > I wrote this code (untested) and it feels a bit much: > > if (dp_lanes == 1) { > if (lane_assignments[0] == 1) { > pr_warn("Lane 0 to physical pin 1 not suggested\n"); > } else if (lane_assignments[0] != 0) { > pr_err("Unsupported logical to physical pin mapping\n"); > return -EINVAL; > } > } else if (dp_lanes == 2 || dp_lanes == 4) { > u8 good_mask = dp_lanes == 2 ? 0x3 : 0xf; > u8 mask = 0; > > for (i = 0; i < dp_lanes; i++) > mask |= BIT(lane_assignments[i]) > > if (mask != good_mask) { > pr_err("Unsupported logical to physical pin mapping\n"); > return -EINVAL; > } > } else { > pr_err("Invalid number of DP lanes: %d\n", dp_lanes); > } > > If you feel strongly I'll add it to the next version. Does anyone > else have any opinions of whether they'd like all that checking or > whether we should just trust the person designing the hardware and > writing the device tree to put the right values in? If we don't want to test that, I would at least document it in the DT bindings. It will be a good occasion to switch the bindings to YAML ;-) -- Regards, Laurent Pinchart
