linux-kernelgpuhdmiimx8

Driving a 137,930 KHz 1080x1920 portrait HDMI screen from an IMX8M

I need to make a fixed-frequency screen (with a new custom mode line):

{ DRM_MODE("1080x1920", DRM_MODE_TYPE_DRIVER, 137930,
            1080, 1140, 1150, 1185, 0,
            1920, 1928, 1932, 1940, 0,
            DRM_MODE_FLAG_NHSYNC | DRM_MODE_FLAG_NVSYNC),
            .vrefresh = 60, .picture_aspect_ratio = HDMI_PICTURE_ASPECT_16_9, },

(in edid_cea_modes[] in imx-hdp.c) work with the iMX8M.

My problem is that there is no 137,930 KHz mode in

/* Table 8. HDMI TX clock control settings (pixel clock is output) */
const u32 t28hpc_hdmitx_clock_control_table_pixel_out[T28HPC_HDMITX_CLOCK_CONTROL_TABLE_ROWS_PIXEL_OUT][T28HPC_HDMITX_CLOCK_CONTROL_TABLE_COLS_PIXEL_OUT] = {
{ 27000, 1000, 270000, 0x03, 0x1, 0x1, 240, 0x0BC, 0x030, 80, 0x026, 0x026, 2160000, 0, 2, 2, 2, 4, 135000, 0x3, 27000, 1},
{ 27000, 1250, 337500, 0x03, 0x1, 0x1, 300, 0x0EC, 0x03C, 100, 0x030, 0x030, 2700000, 0, 2, 2, 2, 4, 168750, 0x3, 33750, 1},
{ 27000, 1500, 405000, 0x03, 0x1, 0x1, 360, 0x11C, 0x048, 120, 0x03A, 0x03A, 3240000, 0, 2, 2, 2, 4, 202500, 0x3, 40500, 1},
{ 27000, 2000, 540000, 0x03, 0x1, 0x1, 240, 0x0BC, 0x030, 80, 0x026, 0x026, 2160000, 0, 2, 2, 2, 4, 270000, 0x2, 54000, 1},
{ 54000, 1000, 540000, 0x03, 0x1, 0x1, 480, 0x17C, 0x060, 80, 0x026, 0x026, 4320000, 1, 2, 2, 2, 4, 270000, 0x3, 54000, 1},
{ 54000, 1250, 675000, 0x04, 0x1, 0x1, 400, 0x13C, 0x050, 50, 0x017, 0x017, 2700000, 0, 1, 1, 2, 4, 337500, 0x2, 67500, 1},
{ 54000, 1500, 810000, 0x04, 0x1, 0x1, 480, 0x17C, 0x060, 60, 0x01C, 0x01C, 3240000, 0, 2, 2, 2, 2, 405000, 0x2, 81000, 1},
{ 54000, 2000, 1080000, 0x03, 0x1, 0x1, 240, 0x0BC, 0x030, 40, 0x012, 0x012, 2160000, 0, 2, 2, 2, 1, 540000, 0x1, 108000, 1},
{ 74250, 1000, 742500, 0x03, 0x1, 0x1, 660, 0x20C, 0x084, 80, 0x026, 0x026, 5940000, 1, 2, 2, 2, 4, 371250, 0x3, 74250, 1},
{ 74250, 1250, 928125, 0x04, 0x1, 0x1, 550, 0x1B4, 0x06E, 50, 0x017, 0x017, 3712500, 1, 1, 1, 2, 4, 464062, 0x2, 92812, 1},
{ 74250, 1500, 1113750, 0x04, 0x1, 0x1, 660, 0x20C, 0x084, 60, 0x01C, 0x01C, 4455000, 1, 2, 2, 2, 2, 556875, 0x2, 111375, 1},
{ 74250, 2000, 1485000, 0x03, 0x1, 0x1, 330, 0x104, 0x042, 40, 0x012, 0x012, 2970000, 0, 2, 2, 2, 1, 742500, 0x1, 148500, 1},
{ 99000, 1000, 990000, 0x03, 0x1, 0x1, 440, 0x15C, 0x058, 40, 0x012, 0x012, 3960000, 1, 2, 2, 2, 2, 495000, 0x2, 99000, 1},
{ 99000, 1250, 1237500, 0x03, 0x1, 0x1, 275, 0x0D8, 0x037, 25, 0x00B, 0x00A, 2475000, 0, 1, 1, 2, 2, 618750, 0x1, 123750, 1},
{ 99000, 1500, 1485000, 0x03, 0x1, 0x1, 330, 0x104, 0x042, 30, 0x00D, 0x00D, 2970000, 0, 2, 2, 2, 1, 742500, 0x1, 148500, 1},
{ 99000, 2000, 1980000, 0x03, 0x1, 0x1, 440, 0x15C, 0x058, 40, 0x012, 0x012, 3960000, 1, 2, 2, 2, 1, 990000, 0x1, 198000, 1},
{148500, 1000, 1485000, 0x03, 0x1, 0x1, 660, 0x20C, 0x084, 40, 0x012, 0x012, 5940000, 1, 2, 2, 2, 2, 742500, 0x2, 148500, 1},
{148500, 1250, 1856250, 0x04, 0x1, 0x1, 550, 0x1B4, 0x06E, 25, 0x00B, 0x00A, 3712500, 1, 1, 1, 2, 2, 928125, 0x1, 185625, 1},
{148500, 1500, 2227500, 0x03, 0x1, 0x1, 495, 0x188, 0x063, 30, 0x00D, 0x00D, 4455000, 1, 1, 1, 2, 2, 1113750, 0x1, 222750, 1},
{148500, 2000, 2970000, 0x03, 0x1, 0x1, 660, 0x20C, 0x084, 40, 0x012, 0x012, 5940000, 1, 2, 2, 2, 1, 1485000, 0x1, 297000, 1},
{198000, 1000, 1980000, 0x03, 0x1, 0x1, 220, 0x0AC, 0x02C, 10, 0x003, 0x003, 1980000, 0, 1, 1, 2, 1, 990000, 0x0, 198000, 1},
{198000, 1250, 2475000, 0x03, 0x1, 0x1, 550, 0x1B4, 0x06E, 25, 0x00B, 0x00A, 4950000, 1, 1, 1, 2, 2, 1237500, 0x1, 247500, 1},
{198000, 1500, 2970000, 0x03, 0x1, 0x1, 330, 0x104, 0x042, 15, 0x006, 0x005, 2970000, 0, 1, 1, 2, 1, 1485000, 0x0, 297000, 1},
{198000, 2000, 3960000, 0x03, 0x1, 0x1, 440, 0x15C, 0x058, 20, 0x008, 0x008, 3960000, 1, 1, 1, 2, 1, 1980000, 0x0, 396000, 1},
{297000, 1000, 2970000, 0x03, 0x1, 0x1, 330, 0x104, 0x042, 10, 0x003, 0x003, 2970000, 0, 1, 1, 2, 1, 1485000, 0x0, 297000, 1},
{297000, 1500, 4455000, 0x03, 0x1, 0x1, 495, 0x188, 0x063, 15, 0x006, 0x005, 4455000, 1, 1, 1, 2, 1, 2227500, 0x0, 445500, 1},
{297000, 2000, 5940000, 0x03, 0x1, 0x1, 660, 0x20C, 0x084, 20, 0x008, 0x008, 5940000, 1, 1, 1, 2, 1, 2970000, 0x0, 594000, 1},
{594000, 1000, 5940000, 0x03, 0x1, 0x1, 660, 0x20C, 0x084, 10, 0x003, 0x003, 5940000, 1, 1, 1, 2, 1, 2970000, 0x0, 594000, 1},
{594000, 750, 4455000, 0x03, 0x1, 0x1, 495, 0x188, 0x063, 10, 0x003, 0x003, 4455000, 1, 1, 1, 2, 1, 2227500, 0x0, 445500, 0},
{594000, 625, 3712500, 0x04, 0x1, 0x1, 550, 0x1B4, 0x06E, 10, 0x003, 0x003, 3712500, 1, 1, 1, 2, 1, 1856250, 0x0, 371250, 0},
{594000, 500, 2970000, 0x03, 0x1, 0x1, 660, 0x20C, 0x084, 10, 0x003, 0x003, 5940000, 1, 1, 1, 2, 2, 1485000, 0x1, 297000, 1},

in t28hpc_hdmitx_table.c.

I need to learn:

  1. Is the table the full extent of what the GPU/DCSS can do? (In which case it can't drive my 1080x1920 portrait screen.)

  2. If 137,930 KHz modes are physically possible in the DCSS, where do I get the other numbers from? (I assume that they're register settings.)

Solution

  • I've made this work.

    The first step was to add a new row to t28hpc_hdmitx_clock_control_table_pixel_out[][] in drivers/gpu/drm/imx/hdp/t28hpc_hdmitx_table.c:

    {138375, 1000, 1383750, 0x03, 0x1, 0x1, 615, 0x1E8, 0x07B, 40, 0x012, 0x012, 5535000, 1, 2, 2, 2, 2, 691875, 0x2, 138375, 1},

    I generated these values with a day of staring at this table and finding patterns. Hint: one relation between fields involves a + 4 modification.

    This still failed, but now with the error:

    [    2.147134] [drm] API_AFE_t28hpc_hdmitx.c:406 pixel_freq_khz: 138375, feedback_factor: 1000
[    2.155556] [drm] API_AFE_t28hpc_hdmitx.c:409 Pixel clock frequency (138375 KHz) is supported in this color depth (8-bit). Settings found in row 16
[    2.168785] [drm] VCO frequency is 5535000
[    2.172900] [drm] API_AFE_t28hpc_hdmitx.c:499 VCO frequency (5535000 KHz) not supported
[    2.180925] [drm:hdmi_phy_init_t28hpc] *ERROR* failed to set phy pclock
[    2.187557] [drm:imx_hdp_imx_bind] *ERROR* Failed to initialise HDP PHY

    I fixed this by the modifying a row in t28hpc_hdmitx_pll_tuning_table_pixel_out[][] from:

    {11, 4950000, 4950000, 0x6, 0x3, 0x1, 0x00, 0x07,  550, 0x42, 213, 7, 258},

    to

    {11, 5535000, 5535000, 0x6, 0x3, 0x1, 0x00, 0x07,  615, 0x42, 213, 7, 258},

    All that was required was to change instances of 4950000 to 5535000 and 550 to 615 to account for the frequency differences.

    I've ended up with a screen that runs 0.3% too fast, due to there being no integer solutions which yield exactly 137,930 KHz, but that's better than a black screen.

    With a few hours' additional work, I can probably tweak the porches to get 60Hz at a 138,375 KHz pixel clock.

    1080x1920 HDMI screen working