phy: dphy: Correct clk_pre parameter

The D-PHY specification (v1.2) explicitly mentions that the T-CLK-PRE
parameter's unit is Unit Interval(UI) and the minimum value is 8.  Also,
kernel doc of the 'clk_pre' member of struct phy_configure_opts_mipi_dphy
mentions that it should be in UI.  However, the dphy core driver wrongly
sets 'clk_pre' to 8000, which seems to hint that it's in picoseconds.

So, let's fix the dphy core driver to correctly reflect the T-CLK-PRE
parameter's minimum value according to the D-PHY specification.

I'm assuming that all impacted custom drivers shall program values in
TxByteClkHS cycles into hardware for the T-CLK-PRE parameter.  The D-PHY
specification mentions that the frequency of TxByteClkHS is exactly 1/8
the High-Speed(HS) bit rate(each HS bit consumes one UI).  So, relevant
custom driver code is changed to program those values as
DIV_ROUND_UP(cfg->clk_pre, BITS_PER_BYTE), then.

Note that I've only tested the patch with RM67191 DSI panel on i.MX8mq EVK.
Help is needed to test with other i.MX8mq, Meson and Rockchip platforms,
as I don't have the hardwares.

Fixes: 2ed869990e14 ("phy: Add MIPI D-PHY configuration options")
Tested-by: Liu Ying <victor.liu@nxp.com> # RM67191 DSI panel on i.MX8mq EVK
Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com> # for phy-meson-axg-mipi-dphy.c
Tested-by: Neil Armstrong <narmstrong@baylibre.com> # for phy-meson-axg-mipi-dphy.c
Tested-by: Guido Günther <agx@sigxcpu.org> # Librem 5 (imx8mq) with it's rather picky panel
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Liu Ying <victor.liu@nxp.com>
Link: https://lore.kernel.org/r/20220124024007.1465018-1-victor.liu@nxp.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

1 files changed, 5 insertions, 7 deletions

diff --git a/drivers/gpu/drm/bridge/nwl-dsi.c b/drivers/gpu/drm/bridge/nwl-dsi.c
index a7389a0facfb..af07eeb47ca0 100644
--- a/drivers/gpu/drm/bridge/nwl-dsi.c
+++ b/drivers/gpu/drm/bridge/nwl-dsi.c
@@ -7,6 +7,7 @@
  */
 
 #include <linux/bitfield.h>
+#include <linux/bits.h>
 #include <linux/clk.h>
 #include <linux/irq.h>
 #include <linux/math64.h>
@@ -196,12 +197,9 @@ static u32 ps2bc(struct nwl_dsi *dsi, unsigned long long ps)
 /*
  * ui2bc - UI time periods to byte clock cycles
  */
-static u32 ui2bc(struct nwl_dsi *dsi, unsigned long long ui)
+static u32 ui2bc(unsigned int ui)
 {
-	u32 bpp = mipi_dsi_pixel_format_to_bpp(dsi->format);
-
-	return DIV64_U64_ROUND_UP(ui * dsi->lanes,
-				  dsi->mode.clock * 1000 * bpp);
+	return DIV_ROUND_UP(ui, BITS_PER_BYTE);
 }
 
 /*
@@ -232,12 +230,12 @@ static int nwl_dsi_config_host(struct nwl_dsi *dsi)
 	}
 
 	/* values in byte clock cycles */
-	cycles = ui2bc(dsi, cfg->clk_pre);
+	cycles = ui2bc(cfg->clk_pre);
 	DRM_DEV_DEBUG_DRIVER(dsi->dev, "cfg_t_pre: 0x%x\n", cycles);
 	nwl_dsi_write(dsi, NWL_DSI_CFG_T_PRE, cycles);
 	cycles = ps2bc(dsi, cfg->lpx + cfg->clk_prepare + cfg->clk_zero);
 	DRM_DEV_DEBUG_DRIVER(dsi->dev, "cfg_tx_gap (pre): 0x%x\n", cycles);
-	cycles += ui2bc(dsi, cfg->clk_pre);
+	cycles += ui2bc(cfg->clk_pre);
 	DRM_DEV_DEBUG_DRIVER(dsi->dev, "cfg_t_post: 0x%x\n", cycles);
 	nwl_dsi_write(dsi, NWL_DSI_CFG_T_POST, cycles);
 	cycles = ps2bc(dsi, cfg->hs_exit);