[PATCH 0/2] MediaTek MT8195 HDMI PHY Fixes

[PATCH 0/2] MediaTek MT8195 HDMI PHY Fixes

[AngeloGioacchino Del Regno]

This series adds two fixes for the MT8195-class HDMI PHY, found in
MT8195, MT8188 and Genio variants.

This is fixing PLL calculation, and TMDS clock dividers, to achieve
all of the modes requiring data rates higher than 3.4Gbps, with the
successfully tested target being 3840x2160@60Hz.

This was tested on MT8395 MediaTek Genio 1200, Radxa NIO-12L and on
MT8390 MediaTek Genio 700, with 3 different HDMI displays (two TVs
and a 4k LG workstation display).

AngeloGioacchino Del Regno (2):
  phy: mediatek: phy-mtk-hdmi-mt8195: Fix PLL calc divisor overflow
  phy: mediatek: phy-mtk-hdmi-mt8195: Fix TMDS clk bit ratio setting

 drivers/phy/mediatek/phy-mtk-hdmi-mt8195.c | 4 ++--
 drivers/phy/mediatek/phy-mtk-hdmi-mt8195.h | 3 +++
 2 files changed, 5 insertions(+), 2 deletions(-)

-- 
2.54.0


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[PATCH 1/2] phy: mediatek: phy-mtk-hdmi-mt8195: Fix PLL calc divisor overflow

[AngeloGioacchino Del Regno]

When trying to calculate a PLL rate for target display resolutions
above 2560x1440, 24bpp, 30Hz, the pixel clock value will be more
than 32-bits long but the division to finally calculate the digital
clock divider is being done with div_u64(), which expects a 32bit
unsigned divisor.

Fix the overflow by using div64_u64() instead.

Fixes: 9d9ff3d2a4a5 ("phy: mediatek: hdmi: mt8195: fix wrong pll calculus")
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
---
 drivers/phy/mediatek/phy-mtk-hdmi-mt8195.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/phy/mediatek/phy-mtk-hdmi-mt8195.c b/drivers/phy/mediatek/phy-mtk-hdmi-mt8195.c
index 1426a2db984d..e6ee8e080022 100644
--- a/drivers/phy/mediatek/phy-mtk-hdmi-mt8195.c
+++ b/drivers/phy/mediatek/phy-mtk-hdmi-mt8195.c
@@ -290,7 +290,7 @@ static int mtk_hdmi_pll_calc(struct mtk_hdmi_phy *hdmi_phy, struct clk_hw *hw,
 	posdiv2 = 1;
 
 	/* Digital clk divider, max /32 */
-	digital_div = div_u64(ns_hdmipll_ck, posdiv1 * posdiv2 * pixel_clk);
+	digital_div = div64_u64(ns_hdmipll_ck, posdiv1 * posdiv2 * pixel_clk);
 	if (!(digital_div <= 32 && digital_div >= 1))
 		return -EINVAL;
 
-- 
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Re: [PATCH 1/2] phy: mediatek: phy-mtk-hdmi-mt8195: Fix PLL calc divisor overflow

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [High] Calculations using `14835 * MEGA`, `5 * GIGA`, and `12 * GIGA` silently overflow 32-bit `unsigned long` types on 32-bit architectures, completely breaking clock tiering and boundary checks.
--

commit 8179a32cf1dac8f1d080e57bbce79246661b50eb
Author: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>

phy: mediatek: phy-mtk-hdmi-mt8195: Fix PLL calc divisor overflow

This commit fixes an issue where calculating a PLL rate for high display
resolutions results in a pixel clock exceeding 32 bits, but the digital
clock divider calculation uses div_u64(), which expects a 32-bit divisor.
It resolves this by using div64_u64() instead to prevent overflow.

> diff --git a/drivers/phy/mediatek/phy-mtk-hdmi-mt8195.c b/drivers/phy/mediatek/phy-mtk-hdmi-mt8195.c
> index 1426a2db984d5..e6ee8e0800222 100644
> --- a/drivers/phy/mediatek/phy-mtk-hdmi-mt8195.c
> +++ b/drivers/phy/mediatek/phy-mtk-hdmi-mt8195.c
> @@ -290,7 +290,7 @@ static int mtk_hdmi_pll_calc(struct mtk_hdmi_phy *hdmi_phy, struct clk_hw *hw,

[Severity: High]
This is a pre-existing issue, but do the constants in this function silently
overflow on 32-bit architectures?

Earlier in mtk_hdmi_pll_calc(), there are tier threshold calculations like:

    else if ((tmds_clk * 100) >= 14835 * MEGA && (tmds_clk * 10) < 2967 * MEGA)

and later boundary checks:

    if (ns_hdmipll_ck >= 5 * GIGA &&
        ns_hdmipll_ck <= 12 * GIGA)

If MEGA and GIGA evaluate as 32-bit types on 32-bit systems, a multiplication
like 14835 * MEGA evaluates to 14,835,000,000, which wraps around modulo 2^32
to 1,950,098,112 before being promoted to u64 for the comparison against
tmds_clk * 100.

Similarly, 5 * GIGA and 12 * GIGA would overflow, potentially rendering the
valid PLL clock range mathematically unreachable and forcing the function to
always return -EINVAL on 32-bit builds.

Should these constants be explicitly typed or cast to u64 to ensure the
comparisons work correctly on 32-bit kernels?

>  	posdiv2 = 1;
>  
>  	/* Digital clk divider, max /32 */
> -	digital_div = div_u64(ns_hdmipll_ck, posdiv1 * posdiv2 * pixel_clk);
> +	digital_div = div64_u64(ns_hdmipll_ck, posdiv1 * posdiv2 * pixel_clk);
>  	if (!(digital_div <= 32 && digital_div >= 1))
>  		return -EINVAL;
>

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260701121936.19407-1-angelogioacchino.delregno@collabora.com?part=1

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[PATCH 2/2] phy: mediatek: phy-mtk-hdmi-mt8195: Fix TMDS clk bit ratio setting

[AngeloGioacchino Del Regno]

The comment in the mtk_phy_tmds_clk_ratio() function clearly and
correctly explains that the TMDS ratio has to be 1/10 for data
rates under 3.4Gbps, and 1/40 over that.

Unfortunately though, the TXC_DIV register setting was wrong, as
in value 3 means to divide by 8 and, in order to achieve the in
spec 1/40 (tmds) data rate, this has to divide by 4 instead!
In order to achieve the correct 1/40 (tmds) data rate, this has

Add definitions for the TXC_DIV register values clearly explaining
the meanings (DIV2, DIV4, DIV8), and program the correct, DIV 4,
value to the register in mtk_phy_tmds_clk_ratio().

This fixes out of spec clocking and, with this change, SoCs using
the MT8195 class HDMI PHYs can now successfully be configured to
output 3840x2160@60Hz over HDMI.

Fixes: 45810d486bb4 ("phy: mediatek: add support for phy-mtk-hdmi-mt8195")
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
---
 drivers/phy/mediatek/phy-mtk-hdmi-mt8195.c | 2 +-
 drivers/phy/mediatek/phy-mtk-hdmi-mt8195.h | 3 +++
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/phy/mediatek/phy-mtk-hdmi-mt8195.c b/drivers/phy/mediatek/phy-mtk-hdmi-mt8195.c
index e6ee8e080022..a4bc1268946d 100644
--- a/drivers/phy/mediatek/phy-mtk-hdmi-mt8195.c
+++ b/drivers/phy/mediatek/phy-mtk-hdmi-mt8195.c
@@ -36,7 +36,7 @@ mtk_phy_tmds_clk_ratio(struct mtk_hdmi_phy *hdmi_phy, bool enable)
 	 * clock bit ratio 1:40, under 3.4Gbps, clock bit ratio 1:10
 	 */
 	if (enable)
-		mtk_phy_update_field(regs + HDMI20_CLK_CFG, REG_TXC_DIV, 3);
+		mtk_phy_update_field(regs + HDMI20_CLK_CFG, REG_TXC_DIV, VAL_TXC_DIV4);
 	else
 		mtk_phy_clear_bits(regs + HDMI20_CLK_CFG, REG_TXC_DIV);
 }
diff --git a/drivers/phy/mediatek/phy-mtk-hdmi-mt8195.h b/drivers/phy/mediatek/phy-mtk-hdmi-mt8195.h
index e26caaf4d104..58800d7659ca 100644
--- a/drivers/phy/mediatek/phy-mtk-hdmi-mt8195.h
+++ b/drivers/phy/mediatek/phy-mtk-hdmi-mt8195.h
@@ -17,6 +17,9 @@
 
 #define HDMI20_CLK_CFG 0x70
 #define REG_TXC_DIV GENMASK(31, 30)
+#define VAL_TXC_DIV2 1
+#define VAL_TXC_DIV4 2
+#define VAL_TXC_DIV8 3
 
 #define HDMI_1_CFG_0 0x00
 #define RG_HDMITX21_DRV_IBIAS_CLK GENMASK(10, 5)
-- 
2.54.0


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