linux-kernel - Re: [PATCH 2/2] PCI: layerscape: Add the workaround for lost link capablities during reset

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Message-ID: <20230718050359.GA4771@thinkpad>
Date:   Tue, 18 Jul 2023 10:33:59 +0530
From:   Manivannan Sadhasivam <mani@...nel.org>
To:     Frank Li <Frank.li@....com>
Cc:     Minghuan Lian <minghuan.Lian@....com>,
        Mingkai Hu <mingkai.hu@....com>, Roy Zang <roy.zang@....com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "open list:PCI DRIVER FOR FREESCALE LAYERSCAPE" 
        <linuxppc-dev@...ts.ozlabs.org>,
        "open list:PCI DRIVER FOR FREESCALE LAYERSCAPE" 
        <linux-pci@...r.kernel.org>,
        "moderated list:PCI DRIVER FOR FREESCALE LAYERSCAPE" 
        <linux-arm-kernel@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>, imx@...ts.linux.dev
Subject: Re: [PATCH 2/2] PCI: layerscape: Add the workaround for lost link
 capablities during reset

On Mon, Jul 17, 2023 at 02:45:23PM -0400, Frank Li wrote:
> On Mon, Jul 17, 2023 at 09:29:10PM +0530, Manivannan Sadhasivam wrote:
> > On Thu, Jun 15, 2023 at 12:41:12PM -0400, Frank Li wrote:
> > > From: Xiaowei Bao <xiaowei.bao@....com>
> > > 
> > > A workaround for the issue where the PCI Express Endpoint (EP) controller
> > > loses the values of the Maximum Link Width and Supported Link Speed from
> > > the Link Capabilities Register, which initially configured by the Reset
> > > Configuration Word (RCW) during a link-down or hot reset event.
> > > 
> > 
> > If this fixes an issue, then there should be a Fixes tag.
> 
> It is not fixed a exist software issue, just workaround a hardwre errata.
> 

But the hardware errata is there from the start, right? So technically this
driver doesn't address that so far and so this patch looks like a fix to me.

Plus adding a fixes tag and CCing stable list will allow this patch to be
backported to stable kernels.

- Mani

> > 
> > > Signed-off-by: Xiaowei Bao <xiaowei.bao@....com>
> > > Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@....com>
> > > Signed-off-by: Frank Li <Frank.Li@....com>
> > > ---
> > >  drivers/pci/controller/dwc/pci-layerscape-ep.c | 13 +++++++++++++
> > >  1 file changed, 13 insertions(+)
> > > 
> > > diff --git a/drivers/pci/controller/dwc/pci-layerscape-ep.c b/drivers/pci/controller/dwc/pci-layerscape-ep.c
> > > index 4e4fdd1dfea7..2ef02d827eeb 100644
> > > --- a/drivers/pci/controller/dwc/pci-layerscape-ep.c
> > > +++ b/drivers/pci/controller/dwc/pci-layerscape-ep.c
> > > @@ -45,6 +45,7 @@ struct ls_pcie_ep {
> > >  	struct pci_epc_features		*ls_epc;
> > >  	const struct ls_pcie_ep_drvdata *drvdata;
> > >  	int				irq;
> > > +	u32				lnkcap;
> > >  	bool				big_endian;
> > >  };
> > >  
> > > @@ -73,6 +74,7 @@ static irqreturn_t ls_pcie_ep_event_handler(int irq, void *dev_id)
> > >  	struct ls_pcie_ep *pcie = dev_id;
> > >  	struct dw_pcie *pci = pcie->pci;
> > >  	u32 val, cfg;
> > > +	u8 offset;
> > >  
> > >  	val = ls_lut_readl(pcie, PEX_PF0_PME_MES_DR);
> > >  	ls_lut_writel(pcie, PEX_PF0_PME_MES_DR, val);
> > > @@ -81,6 +83,13 @@ static irqreturn_t ls_pcie_ep_event_handler(int irq, void *dev_id)
> > >  		return IRQ_NONE;
> > >  
> > >  	if (val & PEX_PF0_PME_MES_DR_LUD) {
> > > +
> > 
> > Please add a comment on why the LNKCAP is being restored here.
> > 
> > > +		offset = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
> > > +
> > > +		dw_pcie_dbi_ro_wr_en(pci);
> > > +		dw_pcie_writew_dbi(pci, offset + PCI_EXP_LNKCAP, pcie->lnkcap);
> > 
> > lnkcap is a 32-bit variable, so you should use dw_pcie_writel_dbi().
> > 
> > - Mani
> > 
> > > +		dw_pcie_dbi_ro_wr_dis(pci);
> > > +
> > >  		cfg = ls_lut_readl(pcie, PEX_PF0_CONFIG);
> > >  		cfg |= PEX_PF0_CFG_READY;
> > >  		ls_lut_writel(pcie, PEX_PF0_CONFIG, cfg);
> > > @@ -216,6 +225,7 @@ static int __init ls_pcie_ep_probe(struct platform_device *pdev)
> > >  	struct ls_pcie_ep *pcie;
> > >  	struct pci_epc_features *ls_epc;
> > >  	struct resource *dbi_base;
> > > +	u8 offset;
> > >  	int ret;
> > >  
> > >  	pcie = devm_kzalloc(dev, sizeof(*pcie), GFP_KERNEL);
> > > @@ -252,6 +262,9 @@ static int __init ls_pcie_ep_probe(struct platform_device *pdev)
> > >  
> > >  	platform_set_drvdata(pdev, pcie);
> > >  
> > > +	offset = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
> > > +	pcie->lnkcap = dw_pcie_readl_dbi(pci, offset + PCI_EXP_LNKCAP);
> > > +
> > >  	ret = dw_pcie_ep_init(&pci->ep);
> > >  	if (ret)
> > >  		return ret;
> > > -- 
> > > 2.34.1
> > > 
> > 
> > -- 
> > மணிவண்ணன் சதாசிவம்

-- 
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