linux-kernel - Re: [PATCH 2/2] PCI: qcom-ep: Implement dbi_cs2_access() function callback for DBI CS2 access

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Message-ID: <20231017162129.GF5274@thinkpad>
Date:   Tue, 17 Oct 2023 21:51:29 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Bjorn Andersson <quic_bjorande@...cinc.com>
Cc:     Jingoo Han <jingoohan1@...il.com>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Manivannan Sadhasivam <mani@...nel.org>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH 2/2] PCI: qcom-ep: Implement dbi_cs2_access() function
 callback for DBI CS2 access

On Tue, Oct 17, 2023 at 07:24:31AM -0700, Bjorn Andersson wrote:
> On Tue, Oct 17, 2023 at 11:47:55AM +0530, Manivannan Sadhasivam wrote:
> > From: Manivannan Sadhasivam <mani@...nel.org>
> 
> Your S-o-b should match this.
> 

I gave b4 a shot for sending the patches and missed this. Will fix it in next
version.

> > 
> > Qcom EP platforms require enabling/disabling the DBI CS2 access while
> > programming some read only and shadow registers through DBI. So let's
> > implement the dbi_cs2_access() callback that will be called by the DWC core
> > while programming such registers like BAR mask register.
> > 
> > Without DBI CS2 access, writes to those registers will not be reflected.
> > 
> > Fixes: f55fee56a631 ("PCI: qcom-ep: Add Qualcomm PCIe Endpoint controller driver")
> > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> > ---
> >  drivers/pci/controller/dwc/pcie-qcom-ep.c | 14 ++++++++++++++
> >  1 file changed, 14 insertions(+)
> > 
> > diff --git a/drivers/pci/controller/dwc/pcie-qcom-ep.c b/drivers/pci/controller/dwc/pcie-qcom-ep.c
> > index 32c8d9e37876..4653cbf7f9ed 100644
> > --- a/drivers/pci/controller/dwc/pcie-qcom-ep.c
> > +++ b/drivers/pci/controller/dwc/pcie-qcom-ep.c
> > @@ -124,6 +124,7 @@
> >  
> >  /* ELBI registers */
> >  #define ELBI_SYS_STTS				0x08
> > +#define ELBI_CS2_ENABLE				0xa4
> >  
> >  /* DBI registers */
> >  #define DBI_CON_STATUS				0x44
> > @@ -262,6 +263,18 @@ static void qcom_pcie_dw_stop_link(struct dw_pcie *pci)
> >  	disable_irq(pcie_ep->perst_irq);
> >  }
> >  
> > +static void qcom_pcie_dbi_cs2_access(struct dw_pcie *pci, bool enable)
> > +{
> > +	struct qcom_pcie_ep *pcie_ep = to_pcie_ep(pci);
> > +
> > +	writel_relaxed(enable, pcie_ep->elbi + ELBI_CS2_ENABLE);
> 
> Don't you want to maintain the ordering of whatever write came before
> this?
> 

Since this in a dedicated function, I did not care about the ordering w.r.t
previous writes. Even if it gets inlined, the order should not matter since it
only enables/disables the CS2 access for the forthcoming writes.

- Mani

> Regards,
> Bjorn
> 
> > +	/*
> > +	 * Do a dummy read to make sure that the previous write has reached the
> > +	 * memory before returning.
> > +	 */
> > +	readl_relaxed(pcie_ep->elbi + ELBI_CS2_ENABLE);
> > +}
> > +
> >  static void qcom_pcie_ep_icc_update(struct qcom_pcie_ep *pcie_ep)
> >  {
> >  	struct dw_pcie *pci = &pcie_ep->pci;
> > @@ -500,6 +513,7 @@ static const struct dw_pcie_ops pci_ops = {
> >  	.link_up = qcom_pcie_dw_link_up,
> >  	.start_link = qcom_pcie_dw_start_link,
> >  	.stop_link = qcom_pcie_dw_stop_link,
> > +	.dbi_cs2_access = qcom_pcie_dbi_cs2_access,
> >  };
> >  
> >  static int qcom_pcie_ep_get_io_resources(struct platform_device *pdev,
> > 
> > -- 
> > 2.25.1
> > 

-- 
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