linux-kernel - Re: [PATCH] phy: qcom-qmp: Correct READY

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Message-ID: <20190612173436.GZ4814@minitux>
Date:   Wed, 12 Jun 2019 10:34:36 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Niklas Cassel <niklas.cassel@...aro.org>
Cc:     Kishon Vijay Abraham I <kishon@...com>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org, Evan Green <evgreen@...omium.org>,
        Marc Gonzalez <marc.w.gonzalez@...e.fr>,
        Vivek Gautam <vivek.gautam@...eaurora.org>
Subject: Re: [PATCH] phy: qcom-qmp: Correct READY_STATUS poll break condition

On Wed 12 Jun 06:08 PDT 2019, Niklas Cassel wrote:

> On Tue, Jun 04, 2019 at 04:24:43PM -0700, Bjorn Andersson wrote:
> > After issuing a PHY_START request to the QMP, the hardware documentation
> > states that the software should wait for the PCS_READY_STATUS to become
> > 1.
> > 
> > With the introduction of c9b589791fc1 ("phy: qcom: Utilize UFS reset
> > controller") an additional 1ms delay was introduced between the start
> > request and the check of the status bit. This greatly increases the
> > chances for the hardware to actually becoming ready before the status
> > bit is read.
> > 
> > The result can be seen in that UFS PHY enabling is now reported as a
> > failure in 10% of the boots on SDM845, which is a clear regression from
> > the previous rare/occasional failure.
> > 
> > This patch fixes the "break condition" of the poll to check for the
> > correct state of the status bit.
> > 
> > Unfortunately PCIe on 8996 and 8998 does not specify the mask_pcs_ready
> > register, which means that the code checks a bit that's always 0. So the
> > patch also fixes these, in order to not regress these targets.
> > 
> > Cc: stable@...r.kernel.org
> > Cc: Evan Green <evgreen@...omium.org>
> > Cc: Marc Gonzalez <marc.w.gonzalez@...e.fr>
> > Cc: Vivek Gautam <vivek.gautam@...eaurora.org>
> > Fixes: 73d7ec899bd8 ("phy: qcom-qmp: Add msm8998 PCIe QMP PHY support")
> > Fixes: e78f3d15e115 ("phy: qcom-qmp: new qmp phy driver for qcom-chipsets")
> > Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
> > ---
> > 
> > @Kishon, this is a regression spotted in v5.2-rc1, so please consider applying
> > this towards v5.2.
> > 
> >  drivers/phy/qualcomm/phy-qcom-qmp.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/phy/qualcomm/phy-qcom-qmp.c b/drivers/phy/qualcomm/phy-qcom-qmp.c
> > index cd91b4179b10..43abdfd0deed 100644
> > --- a/drivers/phy/qualcomm/phy-qcom-qmp.c
> > +++ b/drivers/phy/qualcomm/phy-qcom-qmp.c
> > @@ -1074,6 +1074,7 @@ static const struct qmp_phy_cfg msm8996_pciephy_cfg = {
> >  
> >  	.start_ctrl		= PCS_START | PLL_READY_GATE_EN,
> >  	.pwrdn_ctrl		= SW_PWRDN | REFCLK_DRV_DSBL,
> > +	.mask_pcs_ready		= PHYSTATUS,
> >  	.mask_com_pcs_ready	= PCS_READY,
> >  
> >  	.has_phy_com_ctrl	= true,
> > @@ -1253,6 +1254,7 @@ static const struct qmp_phy_cfg msm8998_pciephy_cfg = {
> >  
> >  	.start_ctrl             = SERDES_START | PCS_START,
> >  	.pwrdn_ctrl		= SW_PWRDN | REFCLK_DRV_DSBL,
> > +	.mask_pcs_ready		= PHYSTATUS,
> >  	.mask_com_pcs_ready	= PCS_READY,
> >  };
> >  
> > @@ -1547,7 +1549,7 @@ static int qcom_qmp_phy_enable(struct phy *phy)
> >  	status = pcs + cfg->regs[QPHY_PCS_READY_STATUS];
> >  	mask = cfg->mask_pcs_ready;
> >  
> > -	ret = readl_poll_timeout(status, val, !(val & mask), 1,
> > +	ret = readl_poll_timeout(status, val, val & mask, 1,
> >  				 PHY_INIT_COMPLETE_TIMEOUT);
> >  	if (ret) {
> >  		dev_err(qmp->dev, "phy initialization timed-out\n");
> > -- 
> > 2.18.0
> > 
> 
> msm8996_pciephy_cfg and msm8998_pciephy_cfg not having a bit mask defined
> for PCS ready is really a separate bug, so personally I would have created
> two patches, one that adds the missing masks, and one patch that fixes the
> broken break condition.
> 

We can't add mask_pcs_ready in a separate commit after the poll change,
because this would introduce a regression in the history and we can't
add the mask_pcs_ready before because when I tested this on db820c I saw
occasional initialization failures.

I was not able to verify 8998, but I presume that the same dependency
exists there.

> Either way:
> 
> Reviewed-by: Niklas Cassel <niklas.cassel@...aro.org>

Thanks,
Bjorn