linux-kernel - Re: [PATCH v2] PCI: mediatek-gen3: Disable DVFSRC voltage request

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Date:   Wed, 13 Oct 2021 14:02:26 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Jianjun Wang <jianjun.wang@...iatek.com>
Cc:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Ryder Lee <ryder.lee@...iatek.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        linux-pci@...r.kernel.org, linux-mediatek@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        qizhong.cheng@...iatek.com, Ryan-JH.Yu@...iatek.com,
        Tzung-Bi Shih <tzungbi@...gle.com>
Subject: Re: [PATCH v2] PCI: mediatek-gen3: Disable DVFSRC voltage request

On Wed, Oct 13, 2021 at 01:35:17PM -0500, Bjorn Helgaas wrote:
> On Wed, Oct 13, 2021 at 03:53:28PM +0800, Jianjun Wang wrote:
> > When the DVFSRC feature is not implemented, the MAC layer will
> > assert a voltage request signal when exit from the L1ss state,
> > but cannot receive the voltage ready signal, which will cause
> > the link to fail to exit the L1ss state correctly.
> > 
> > Disable DVFSRC voltage request by default, we need to find
> > a common way to enable it in the future.
> 
> Rewrap commit log to fill 75 columns.
> 
> Does "L1ss" above refer to L1.1 and L1.2?  If so, please say that
> explicitly or say something like "L1 PM Substates" (the term used in
> the PCIe spec) so it's clear.
> 
> This seems on the boundary of PCIe-specified things and Mediatek
> implementation details, so I'm not sure what "DVFSRC," "MAC," and
> "voltage request signal" mean.  Since I don't recognize those terms,
> I'm guessing they are Mediatek-specific things.
> 
> But if they are things specified by the PCIe spec, please use the
> exact names used in the spec.
> 
> > Signed-off-by: Jianjun Wang <jianjun.wang@...iatek.com>
> > Reviewed-by: Tzung-Bi Shih <tzungbi@...gle.com>
> > Tested-by: Qizhong Cheng <qizhong.cheng@...iatek.com>

Krzysztof also pointed out that if this is a bug fix, we may want a
stable tag here.  And, ideally, a Fixes: tag with the specific commit
that introduced the bug.

> > ---
> >  drivers/pci/controller/pcie-mediatek-gen3.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/drivers/pci/controller/pcie-mediatek-gen3.c b/drivers/pci/controller/pcie-mediatek-gen3.c
> > index f3aeb8d4eaca..79fb12fca6a9 100644
> > --- a/drivers/pci/controller/pcie-mediatek-gen3.c
> > +++ b/drivers/pci/controller/pcie-mediatek-gen3.c
> > @@ -79,6 +79,9 @@
> >  #define PCIE_ICMD_PM_REG		0x198
> >  #define PCIE_TURN_OFF_LINK		BIT(4)
> >  
> > +#define PCIE_MISC_CTRL_REG		0x348
> > +#define PCIE_DISABLE_DVFSRC_VLT_REQ	BIT(1)
> > +
> >  #define PCIE_TRANS_TABLE_BASE_REG	0x800
> >  #define PCIE_ATR_SRC_ADDR_MSB_OFFSET	0x4
> >  #define PCIE_ATR_TRSL_ADDR_LSB_OFFSET	0x8
> > @@ -297,6 +300,11 @@ static int mtk_pcie_startup_port(struct mtk_pcie_port *port)
> >  	val &= ~PCIE_INTX_ENABLE;
> >  	writel_relaxed(val, port->base + PCIE_INT_ENABLE_REG);
> >  
> > +	/* Disable DVFSRC voltage request */
> > +	val = readl_relaxed(port->base + PCIE_MISC_CTRL_REG);
> > +	val |= PCIE_DISABLE_DVFSRC_VLT_REQ;
> > +	writel_relaxed(val, port->base + PCIE_MISC_CTRL_REG);
> > +
> >  	/* Assert all reset signals */
> >  	val = readl_relaxed(port->base + PCIE_RST_CTRL_REG);
> >  	val |= PCIE_MAC_RSTB | PCIE_PHY_RSTB | PCIE_BRG_RSTB | PCIE_PE_RSTB;
> > -- 
> > 2.25.1
> >