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

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Message-ID: <cc63872f-3ad5-479e-bfff-8d62478e446e@linaro.org>
Date: Tue, 4 Feb 2025 10:20:51 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Dmitry Baryshkov <dmitry.baryshkov@...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 03/02/2025 18:42, Dmitry Baryshkov wrote:
> 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.

There is no header. That's patch #1 and I do not see how changing this
to FIELDPREP is anyhow related to the actual problem being solved here.

Best regards,
Krzysztof