[PATCH v3] drivers: phy: cadence: cdns-dphy: Enable lower resolutions in dphy

[Harikrishna Shenoy <h-shenoy@ti.com>]

Enable support for data lane rates between 80-160 Mbps cdns dphy
as mentioned in TRM [0] by setting the pll_opdiv field to 16.
This change enables lower resolutions like 640x480 at 60Hz.

[0]: https://www.ti.com/lit/zip/spruil1
(Table 12-552. DPHY_TX_PLL_CTRL Register Field Descriptions)

Reviewed-by: Udit Kumar <u-kumar1@ti.com>
Reviewed-by: Devarsh Thakkar <devarsht@ti.com>
Signed-off-by: Harikrishna Shenoy <h-shenoy@ti.com>
---
Changes in v3:
- Updated commit message.
- Added Reviewed-by tags.
- Link to v2: https://lore.kernel.org/all/20250806052650.429767-1-h-shenoy@ti.com/

Changes in v2:
- Updated commit message and title.
- Added Reviewed-by tag.
- Link to v1: https://lore.kernel.org/all/1ebb82ea-4b6c-4496-b7c0-17d4168d8ddf@ti.com/

Test log: https://gist.github.com/h-shenoy/3975156baf403a0ff8dbcce5b49b2b89

 drivers/phy/cadence/cdns-dphy.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/phy/cadence/cdns-dphy.c b/drivers/phy/cadence/cdns-dphy.c
index ed87a3970f83..9abed2ece9b0 100644
--- a/drivers/phy/cadence/cdns-dphy.c
+++ b/drivers/phy/cadence/cdns-dphy.c
@@ -139,7 +139,7 @@ static int cdns_dsi_get_dphy_pll_cfg(struct cdns_dphy *dphy,
 
 	dlane_bps = opts->hs_clk_rate;
 
-	if (dlane_bps > 2500000000UL || dlane_bps < 160000000UL)
+	if (dlane_bps > 2500000000UL || dlane_bps < 80000000UL)
 		return -EINVAL;
 	else if (dlane_bps >= 1250000000)
 		cfg->pll_opdiv = 1;
@@ -149,6 +149,8 @@ static int cdns_dsi_get_dphy_pll_cfg(struct cdns_dphy *dphy,
 		cfg->pll_opdiv = 4;
 	else if (dlane_bps >= 160000000)
 		cfg->pll_opdiv = 8;
+	else if (dlane_bps >= 80000000)
+		cfg->pll_opdiv = 16;
 
 	cfg->pll_fbdiv = DIV_ROUND_UP_ULL(dlane_bps * 2 * cfg->pll_opdiv *
 					  cfg->pll_ipdiv,
-- 
2.34.1