linux-kernel - Re: [PATCH v2 1/4] drm/msm/dsi/phy: Protect PHY_CMN_CLK

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Message-ID: <le5kxzhm3b2whxoo3eblkelryc7ak2yezugqti2sxw7m244dzc@nyuhhs53jdup>
Date: Mon, 3 Feb 2025 19:42:19 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc: Rob Clark <robdclark@...il.com>, 
	Abhinav Kumar <quic_abhinavk@...cinc.com>, Sean Paul <sean@...rly.run>, 
	Marijn Suijten <marijn.suijten@...ainline.org>, David Airlie <airlied@...il.com>, 
	Simona Vetter <simona@...ll.ch>, linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org, 
	freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/4] drm/msm/dsi/phy: Protect PHY_CMN_CLK_CFG0 updated
 from driver side

On Mon, Feb 03, 2025 at 06:29:18PM +0100, Krzysztof Kozlowski wrote:
> PHY_CMN_CLK_CFG0 register is updated by the PHY driver and by two
> divider clocks from Common Clock Framework:
> devm_clk_hw_register_divider_parent_hw().  Concurrent access by the
> clocks side is protected with spinlock, however driver's side in
> restoring state is not.  Restoring state is called from
> msm_dsi_phy_enable(), so there could be a path leading to concurrent and
> conflicting updates with clock framework.
> 
> Add missing lock usage on the PHY driver side, encapsulated in its own
> function so the code will be still readable.
> 
> Fixes: 1ef7c99d145c ("drm/msm/dsi: add support for 7nm DSI PHY/PLL")
> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
> ---
>  drivers/gpu/drm/msm/dsi/phy/dsi_phy_7nm.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/dsi/phy/dsi_phy_7nm.c b/drivers/gpu/drm/msm/dsi/phy/dsi_phy_7nm.c
> index 031446c87daec0af3f81df324158311f5a80014e..c164f845653816291ad96c863257f75462ef58e7 100644
> --- a/drivers/gpu/drm/msm/dsi/phy/dsi_phy_7nm.c
> +++ b/drivers/gpu/drm/msm/dsi/phy/dsi_phy_7nm.c
> @@ -372,6 +372,15 @@ static void dsi_pll_enable_pll_bias(struct dsi_pll_7nm *pll)
>  	ndelay(250);
>  }
>  
> +static void dsi_pll_cmn_clk_cfg0_write(struct dsi_pll_7nm *pll, u32 val)
> +{
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&pll->postdiv_lock, flags);
> +	writel(val, pll->phy->base + REG_DSI_7nm_PHY_CMN_CLK_CFG0);
> +	spin_unlock_irqrestore(&pll->postdiv_lock, flags);
> +}
> +
>  static void dsi_pll_disable_global_clk(struct dsi_pll_7nm *pll)
>  {
>  	u32 data;
> @@ -574,8 +583,8 @@ static int dsi_7nm_pll_restore_state(struct msm_dsi_phy *phy)
>  	val |= cached->pll_out_div;
>  	writel(val, pll_7nm->phy->pll_base + REG_DSI_7nm_PHY_PLL_PLL_OUTDIV_RATE);
>  
> -	writel(cached->bit_clk_div | (cached->pix_clk_div << 4),
> -	       phy_base + REG_DSI_7nm_PHY_CMN_CLK_CFG0);
> +	dsi_pll_cmn_clk_cfg0_write(pll_7nm,
> +				   cached->bit_clk_div | (cached->pix_clk_div << 4));

Ideally this would be FIELD_PREP or a special function generated for you
in the header.

>  
>  	val = readl(phy_base + REG_DSI_7nm_PHY_CMN_CLK_CFG1);
>  	val &= ~0x3;
> 
> -- 
> 2.43.0
> 

-- 
With best wishes
Dmitry