Re: [PATCH] phy: qcom: qmp-combo: Fix VCO div offset on v3

From: Johan Hovold <johan@kernel.org>
To: Stephen Boyd <swboyd@chromium.org>
Cc: Vinod Koul <vkoul@kernel.org>,
	Kishon Vijay Abraham I <kishon@kernel.org>,
	linux-kernel@vger.kernel.org, patches@lists.linux.dev,
	linux-arm-msm@vger.kernel.org,
	Konrad Dybcio <konrad.dybcio@linaro.org>,
	Bjorn Andersson <andersson@kernel.org>,
	linux-phy@lists.infradead.org,
	Neil Armstrong <neil.armstrong@linaro.org>,
	freedreno@lists.freedesktop.org,
	Douglas Anderson <dianders@chromium.org>,
	Abhinav Kumar <quic_abhinavk@quicinc.com>,
	Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Subject: Re: [PATCH] phy: qcom: qmp-combo: Fix VCO div offset on v3
Date: Mon, 8 Apr 2024 11:46:17 +0200	[thread overview]
Message-ID: <ZhO86VWkrOSIGBHV@hovoldconsulting.com> (raw)
In-Reply-To: <20240404234345.1446300-1-swboyd@chromium.org>

On Thu, Apr 04, 2024 at 04:43:44PM -0700, Stephen Boyd wrote:
> Commit ec17373aebd0 ("phy: qcom: qmp-combo: extract common function to
> setup clocks") changed the offset that is used to write to
> DP_PHY_VCO_DIV from QSERDES_V3_DP_PHY_VCO_DIV to
> QSERDES_V4_DP_PHY_VCO_DIV. Unfortunately, this offset is different
> between v3 and v4 phys:
> 
>  #define QSERDES_V3_DP_PHY_VCO_DIV                 0x064
>  #define QSERDES_V4_DP_PHY_VCO_DIV                 0x070
> 
> meaning that we write the wrong register on v3 phys now. Add another
> generic register to 'regs' and use it here instead of a version specific
> define to fix this.
> 
> This was discovered after Abhinav looked over register dumps with me
> from sc7180 Trogdor devices that started failing to light up the
> external display with v6.6 based kernels. It turns out that some
> monitors are very specific about their link clk frequency and if the
> default power on reset value is still there the monitor will show a
> blank screen or a garbled display. Other monitors are perfectly happy to
> get a bad clock signal.

> Fixes: ec17373aebd0 ("phy: qcom: qmp-combo: extract common function to setup clocks")
> Signed-off-by: Stephen Boyd <swboyd@chromium.org>
> ---
>  drivers/phy/qualcomm/phy-qcom-qmp-combo.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/phy/qualcomm/phy-qcom-qmp-combo.c b/drivers/phy/qualcomm/phy-qcom-qmp-combo.c
> index 7d585a4bbbba..3b19d8ebf467 100644
> --- a/drivers/phy/qualcomm/phy-qcom-qmp-combo.c
> +++ b/drivers/phy/qualcomm/phy-qcom-qmp-combo.c
> @@ -77,6 +77,7 @@ enum qphy_reg_layout {
>  	QPHY_COM_BIAS_EN_CLKBUFLR_EN,
>  
>  	QPHY_DP_PHY_STATUS,
> +	QPHY_DP_PHY_VCO_DIV,
>  
>  	QPHY_TX_TX_POL_INV,
>  	QPHY_TX_TX_DRV_LVL,
> @@ -102,6 +103,7 @@ static const unsigned int qmp_v3_usb3phy_regs_layout[QPHY_LAYOUT_SIZE] = {
> +	[QPHY_DP_PHY_VCO_DIV]		= QSERDES_V3_DP_PHY_VCO_DIV,

> @@ -126,6 +128,7 @@ static const unsigned int qmp_v45_usb3phy_regs_layout[QPHY_LAYOUT_SIZE] = {
> +	[QPHY_DP_PHY_VCO_DIV]		= QSERDES_V4_DP_PHY_VCO_DIV,

I happened to skim this patch on the list and noticed that you added a
new register abstraction but only updated two tables.

A quick look at the driver reveals that there are currently four such
tables, which means that the v5_5nm (e.g. the Lenovo ThinkPad X13s) and
v6 hardware would now be broken instead as they would write to offset 0.

Clearly the hardware abstraction in this driver leaves a lot to wish
for when it's this fragile, but how can three people including the
maintainer review this change without this being noticed?

I just sent a follow-up fix here:

	https://lore.kernel.org/lkml/20240408093023.506-1-johan+linaro@kernel.org/

> @@ -2184,7 +2188,7 @@ static int qmp_combo_configure_dp_clocks(struct qmp_combo *qmp)
>  		/* Other link rates aren't supported */
>  		return -EINVAL;
>  	}
> -	writel(phy_vco_div, qmp->dp_dp_phy + QSERDES_V4_DP_PHY_VCO_DIV);
> +	writel(phy_vco_div, qmp->dp_dp_phy + cfg->regs[QPHY_DP_PHY_VCO_DIV]);

Johan

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