Or at least try to do this. With the possibility of bi-directional communication, it seems natural to expect that MIPI displays should be able to handle automatic configuration for the screen resolution and timings nicely. But the reality is not so pretty.
It appears that the manufacturers of MIPI LCD panels are not very disciplined and do not follow any kind of standard guidelines when it comes to providing the panel identification information. MIPI DSI even has two alternative standard DCS commands for potentially reading the vendor/panel id: MIPI_DCS_GET_DISPLAY_ID and MIPI_DCS_READ_DDB_START. But these commands do not seem to be widely implemented in real hardware. Moreover, the vendors seem to sometimes invent their own custom new commands, while ignoring the standard ones.
This particular patch probes both of the standard DCS panel identification commands and prints the returned raw data to the u-boot console. The standard DCS commands return zero on the MSI Primo81 tablet though, so they are not very usaful in practice. The code for probing additonal non-standard DCS commands is also included (these commands do return something on the MSI Primo81), but commented out for safety reasons.
We don't know what the future brings. Maybe the LCD panels manufacturers are going to start acting responsibly some day. And will implement proper panel identification more often.
Regarding what we have right now. The information retrieval DCS commands still work if reducing the clock speed to the very minimum and enabling only one lane on my MSI Primo81 tablet. Potentially it means that one could perhaps swap two different MIPI LCD panels (if they have a compatible connector) and still have the software handling this fine by doing runtime selection of the right settings (based on checking the panel id).
Signed-off-by: Siarhei Siamashka siarhei.siamashka@gmail.com --- Changes in v2: - Comment out the use of non-standard DCS commands and adjusted the commit message to mention this.
drivers/video/ssd2828.c | 142 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 142 insertions(+)
diff --git a/drivers/video/ssd2828.c b/drivers/video/ssd2828.c index 8b09082..7efe40f 100644 --- a/drivers/video/ssd2828.c +++ b/drivers/video/ssd2828.c @@ -98,6 +98,9 @@ #define SSD2828_CFGR_LPE (1 << 10) #define SSD2828_CFGR_TXD (1 << 11)
+#define SSD2828_ISR_READ_DATA_READY (1 << 0) +#define SSD2828_ISR_BTA_RESPONSE (1 << 2) + #define SSD2828_VIDEO_MODE_NON_BURST_WITH_SYNC_PULSES (0 << 2) #define SSD2828_VIDEO_MODE_NON_BURST_WITH_SYNC_EVENTS (1 << 2) #define SSD2828_VIDEO_MODE_BURST (2 << 2) @@ -167,6 +170,30 @@ static void write_hw_register(const struct ssd2828_config *cfg, u8 regnum, soft_spi_xfer_24bit_3wire(cfg, 0x720000 | val); }
+static int await_completion(const struct ssd2828_config *cfg, + u8 reg, u32 mask, u32 val) +{ + unsigned long tmo = timer_get_us() + 100000; + + while ((read_hw_register(cfg, reg) & mask) != val) { + if (timer_get_us() > tmo) + return 1; + } + return 0; +} + +static int await_bits_set(const struct ssd2828_config *cfg, + u8 reg, u32 val) +{ + return await_completion(cfg, reg, val, val); +} + +static int await_bits_clear(const struct ssd2828_config *cfg, + u8 reg, u32 val) +{ + return await_completion(cfg, reg, val, 0); +} + /* * Send MIPI command to the LCD panel (cmdnum < 0xB0) */ @@ -179,6 +206,79 @@ static void send_mipi_dcs_command(const struct ssd2828_config *cfg, u8 cmdnum) }
/* + * Sends a MIPI DCS command to retrieve information from the LCD panel. + */ +static int send_mipi_dcs_read_command(const struct ssd2828_config *cfg, + u8 cmdnum, + u8 *result_buf, + int bufsize) +{ + int size, i, result = 0; + /* Save CFGR register */ + u32 old_cfgr = read_hw_register(cfg, SSD2828_CFGR); + + /* Set the read enable bit */ + write_hw_register(cfg, SSD2828_CFGR, old_cfgr | SSD2828_CFGR_REN); + /* Clear buffers and bring the state machine to its initial state */ + write_hw_register(cfg, SSD2828_OCR, 1); + if (await_bits_clear(cfg, SSD2828_OCR, 1) != 0) + goto err; + /* Clear the RW1C bits in the ISR register */ + write_hw_register(cfg, SSD2828_ISR, read_hw_register(cfg, SSD2828_ISR)); + + /* Set the payload size (only the DCS command itself) */ + write_hw_register(cfg, SSD2828_PSCR1, 1); + /* Set maximum return size */ + write_hw_register(cfg, SSD2828_MRSR, bufsize); + /* Write the command */ + write_hw_register(cfg, SSD2828_PDR, cmdnum); + + /* Wait for the response */ + if (await_bits_set(cfg, SSD2828_ISR, SSD2828_ISR_BTA_RESPONSE) != 0) + goto err; /* Timeout */ + + /* Check if there is anything in the read buffer */ + if (!(read_hw_register(cfg, SSD2828_ISR) & SSD2828_ISR_READ_DATA_READY)) + goto err; /* There is no data to read */ + + /* The size of the response packet */ + size = read_hw_register(cfg, SSD2828_RDCR); + if (size > bufsize) { + debug("SSD2828: Suspicious packet size.\n"); + size = bufsize; + } + result = size; + + /* + * This is somewhat special and does not seem to be well documented: + * 1) In order to properly read the data, all the buffer must be read + * in one go without any interruptions. For example, using individual + * reads done by the "read_hw_register" function only result in + * repeatedly getting all the same first 16-bits of data without + * advancing. + * 2) In order to empty the buffer, it is necessary to read as much + * data as was initially configured in the MRSR register. The real + * size of the packet in the RDCR register just indicates how much + * of it is actually valid. + */ + soft_spi_xfer_24bit_3wire(cfg, 0x700000 | SSD2828_RR); + for (i = 0; i < (bufsize + 1) / 2; i++) { + u16 data = soft_spi_xfer_24bit_3wire(cfg, 0x730000); + if (size-- > 0) + *result_buf++ = data & 0xFF; + if (size-- > 0) + *result_buf++ = (data >> 8) & 0xFF; + } + + if (read_hw_register(cfg, SSD2828_ISR) & SSD2828_ISR_READ_DATA_READY) + debug("SSD2828: There is still some bogus unread data.\n"); +err: + /* Restore CFGR register */ + write_hw_register(cfg, SSD2828_CFGR, old_cfgr); + return result; +} + +/* * Reset SSD2828 */ static void ssd2828_reset(const struct ssd2828_config *cfg) @@ -337,6 +437,44 @@ static int ssd2828_configure_video_interface(const struct ssd2828_config *cfg, return 0; }
+static void ssd2828_report_dcs_read_result(const struct ssd2828_config *cfg, + u8 cmd) +{ + u8 buf[64]; + int size, i; + size = send_mipi_dcs_read_command(cfg, cmd, buf, sizeof(buf)); + if (size > 0) { + printf("DCS command 0x%02X returned %2d bytes:", cmd, size); + for (i = 0; i < size; i++) + printf(" %02X", buf[i]); + printf("\n"); + } +} + +/* + * Try to use different DCS commands to identify the panel id and + * report it in the log. + */ +static void ssd2828_report_panel_id(const struct ssd2828_config *cfg) +{ + printf("Trying standard MIPI DSI commands to identify LCD panel:\n"); + + ssd2828_report_dcs_read_result(cfg, MIPI_DCS_GET_DISPLAY_ID); + ssd2828_report_dcs_read_result(cfg, MIPI_DCS_READ_DDB_START); + +#if 0 /* May be potentially unsafe, so this block is commented out for now */ + printf("Trying nonstandard MIPI DSI commands to identify LCD panel:\n"); + + /* Used by some LG panels (for example, LH350WS1-SD02.pdf) */ + ssd2828_report_dcs_read_result(cfg, 0xB1); + + /* Used by many LCD panels (for example, DA8620.pdf) */ + ssd2828_report_dcs_read_result(cfg, 0xDA); + ssd2828_report_dcs_read_result(cfg, 0xDB); + ssd2828_report_dcs_read_result(cfg, 0xDC); +#endif +} + int ssd2828_init(const struct ssd2828_config *cfg, const struct ctfb_res_modes *mode) { @@ -425,6 +563,10 @@ int ssd2828_init(const struct ssd2828_config *cfg, send_mipi_dcs_command(cfg, MIPI_DCS_EXIT_SLEEP_MODE); mdelay(cfg->mipi_dsi_delay_after_exit_sleep_mode_ms);
+ /* If it is possible to read back, then try to retrieve the panel id */ + if (cfg->sdo_pin != -1) + ssd2828_report_panel_id(cfg); + send_mipi_dcs_command(cfg, MIPI_DCS_SET_DISPLAY_ON); mdelay(cfg->mipi_dsi_delay_after_set_display_on_ms);