From: Robert Chiras <robert.chiras@xxxxxxx>
The clock-drop-level is needed in order to add more blanking space needed
by DSI panels when sending DSI commands. One level is the equivalent of
phy_ref rate from the PLL rate. Since the PLL rate is targeted as highest
possible, each level should not get the crtc_clock too low, compared to
the actual clock.
Example for a clock of 132M, with "clock-drop-level = <1>" in dts file
will result in a crtc_clock of 129M, using the following logic:
- video_pll rate to provide both phy_ref rate of 24M and pixel-clock
of 132M is 1056M (divisor /43 for phy_ref and /8 for pixel-clock)
- from this rate, we subtract the equivalent of phy_ref (24M) but
keep the same divisor. This way, the video_pll rate will be 1056 - 24
= 1032M.
- new pixel-clock will be: 1032 / 8 = 129M
For a "clock-drop-level = <2>", new pixel-clock will be:
(1056 - (24 * 2)) / 8 = 1008 / 8 = 126M
Signed-off-by: Robert Chiras <robert.chiras@xxxxxxx>
---
drivers/gpu/drm/bridge/nwl-dsi.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)
diff --git a/drivers/gpu/drm/bridge/nwl-dsi.c b/drivers/gpu/drm/bridge/nwl-dsi.c
index 1228466..ac4aa0a 100644
--- a/drivers/gpu/drm/bridge/nwl-dsi.c
+++ b/drivers/gpu/drm/bridge/nwl-dsi.c
@@ -142,6 +142,7 @@ struct nwl_dsi {
struct nwl_dsi_transfer *xfer;
struct list_head valid_modes;
+ u32 clk_drop_lvl;
};
static const struct regmap_config nwl_dsi_regmap_config = {
@@ -842,13 +843,14 @@ static unsigned long nwl_dsi_get_lcm(unsigned long a, unsigned long b)
return ((unsigned long long)a * b) / gcf;
}
-
/*
* This function tries to adjust the crtc_clock for a DSI device in such a way
* that the video pll will be able to satisfy both Display Controller pixel
* clock (feeding out DPI interface) and our input phy_ref clock.
+ * Also, the DC pixel clock must be lower than the actual clock in order to
+ * have enough blanking space to send DSI commands, if the device is a panel.
*/
-static void nwl_dsi_setup_pll_config(struct mode_config *config)
+static void nwl_dsi_setup_pll_config(struct mode_config *config, u32 lvl)
{
unsigned long pll_rate;
int div;
@@ -908,7 +910,6 @@ static void nwl_dsi_setup_pll_config(struct mode_config *config)
}
}
-
/*
* This function will try the required phy speed for current mode
* If the phy speed can be achieved, the phy will save the speed
@@ -1103,7 +1104,7 @@ nwl_dsi_bridge_mode_valid(struct drm_bridge *bridge,
pll_rate = config->pll_rates[config->phy_rate_idx];
if (dsi->pll_clk && !pll_rate)
- nwl_dsi_setup_pll_config(config);
+ nwl_dsi_setup_pll_config(config, dsi->clk_drop_lvl);
return MODE_OK;
}
@@ -1248,6 +1249,7 @@ static const struct drm_bridge_funcs nwl_dsi_bridge_funcs = {
static int nwl_dsi_parse_dt(struct nwl_dsi *dsi)
{
struct platform_device *pdev = to_platform_device(dsi->dev);
+ struct device_node *np = dsi->dev->of_node;
struct clk *clk;
void __iomem *base;
int ret;
@@ -1364,6 +1366,8 @@ static int nwl_dsi_parse_dt(struct nwl_dsi *dsi)
return PTR_ERR(dsi->rst_dpi);
}
+ of_property_read_u32(np, "fsl,clock-drop-level", &dsi->clk_drop_lvl);
+
INIT_LIST_HEAD(&dsi->valid_modes);
return 0;
--
2.7.4
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