linux-kernel - Re: [PATCH 10/11] PCI: qcom-ep: Rework {start/stop}

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Message-ID: <20240326083338.GI9565@thinkpad>
Date: Tue, 26 Mar 2024 14:03:38 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Niklas Cassel <cassel@...nel.org>
Cc: Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	Kishon Vijay Abraham I <kishon@...nel.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Jonathan Hunter <jonathanh@...dia.com>,
	Jingoo Han <jingoohan1@...il.com>,
	Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
	linux-pci@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	linux-kernel@...r.kernel.org, mhi@...ts.linux.dev,
	linux-tegra@...r.kernel.org
Subject: Re: [PATCH 10/11] PCI: qcom-ep: Rework {start/stop}_link() callbacks
 implementation

On Fri, Mar 22, 2024 at 05:10:54PM +0100, Niklas Cassel wrote:
> On Thu, Mar 14, 2024 at 08:53:49PM +0530, Manivannan Sadhasivam wrote:
> > DWC specific start_link() and stop_link() callbacks are supposed to start
> > and stop the link training of the PCIe bus. But the current implementation
> > of this driver enables/disables the PERST# IRQ.
> > 
> > Even though this is not causing any issues, this creates inconsistency
> > among the controller drivers. So for the sake of consistency, let's just
> > start/stop the link training in these callbacks.
> > 
> > Also, PERST# IRQ is now enabled from the start itself, thus allowing the
> > controller driver to initialize the registers when PERST# gets deasserted
> > without waiting for the user intervention though configfs.
> > 
> > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> > ---
> 
> Nice change:
> Reviewed-by: Niklas Cassel <cassel@...nel.org>
> 
> If you dump LTSSM after a PERST assert + deassert,
> using e.g. dw_pcie_readl_dbi(pci, PCIE_PORT_DEBUG1);
> to dump the debug registers (see dw_pcie_link_up())
> do you see that PCIE_PORT_DEBUG1_LINK_IN_TRAINING is set?
> 
> I was thinking that perhaps there was a thought behind
> this original design, that you had to explicitly set
> LTSSM_EN after a fundamental core reset, because it
> would get cleared?
> 

Well, you are right. I was hoping to get an answer from Kishon/Vidya, but you
throwed the light. I will drop these 2 patches.

Thanks!

- Mani

> (It it is implemented like signals and not registers,
> then this change should be fine.)
> 
> 
> Kind regards,
> Niklas
> 
> 
> >  drivers/pci/controller/dwc/pcie-qcom-ep.c | 21 +++++++++++++--------
> >  1 file changed, 13 insertions(+), 8 deletions(-)
> > 
> > diff --git a/drivers/pci/controller/dwc/pcie-qcom-ep.c b/drivers/pci/controller/dwc/pcie-qcom-ep.c
> > index 811f250e967a..653e4ace0a07 100644
> > --- a/drivers/pci/controller/dwc/pcie-qcom-ep.c
> > +++ b/drivers/pci/controller/dwc/pcie-qcom-ep.c
> > @@ -122,6 +122,9 @@
> >  /* PARF_CFG_BITS register fields */
> >  #define PARF_CFG_BITS_REQ_EXIT_L1SS_MSI_LTR_EN	BIT(1)
> >  
> > +/* PARF_LTSSM register fields */
> > +#define LTSSM_EN				BIT(8)
> > +
> >  /* ELBI registers */
> >  #define ELBI_SYS_STTS				0x08
> >  #define ELBI_CS2_ENABLE				0xa4
> > @@ -250,8 +253,12 @@ static int qcom_pcie_dw_link_up(struct dw_pcie *pci)
> >  static int qcom_pcie_dw_start_link(struct dw_pcie *pci)
> >  {
> >  	struct qcom_pcie_ep *pcie_ep = to_pcie_ep(pci);
> > +	u32 val;
> >  
> > -	enable_irq(pcie_ep->perst_irq);
> > +	/* Enable LTSSM */
> > +	val = readl_relaxed(pcie_ep->parf + PARF_LTSSM);
> > +	val |= LTSSM_EN;
> > +	writel_relaxed(val, pcie_ep->parf + PARF_LTSSM);
> >  
> >  	return 0;
> >  }
> > @@ -259,8 +266,12 @@ static int qcom_pcie_dw_start_link(struct dw_pcie *pci)
> >  static void qcom_pcie_dw_stop_link(struct dw_pcie *pci)
> >  {
> >  	struct qcom_pcie_ep *pcie_ep = to_pcie_ep(pci);
> > +	u32 val;
> >  
> > -	disable_irq(pcie_ep->perst_irq);
> > +	/* Disable LTSSM */
> > +	val = readl_relaxed(pcie_ep->parf + PARF_LTSSM);
> > +	val &= ~LTSSM_EN;
> > +	writel_relaxed(val, pcie_ep->parf + PARF_LTSSM);
> >  }
> >  
> >  static void qcom_pcie_dw_write_dbi2(struct dw_pcie *pci, void __iomem *base,
> > @@ -484,11 +495,6 @@ static int qcom_pcie_perst_deassert(struct dw_pcie *pci)
> >  
> >  	dw_pcie_ep_init_notify(&pcie_ep->pci.ep);
> >  
> > -	/* Enable LTSSM */
> > -	val = readl_relaxed(pcie_ep->parf + PARF_LTSSM);
> > -	val |= BIT(8);
> > -	writel_relaxed(val, pcie_ep->parf + PARF_LTSSM);
> > -
> >  	return 0;
> >  
> >  err_disable_resources:
> > @@ -707,7 +713,6 @@ static int qcom_pcie_ep_enable_irq_resources(struct platform_device *pdev,
> >  	}
> >  
> >  	pcie_ep->perst_irq = gpiod_to_irq(pcie_ep->reset);
> > -	irq_set_status_flags(pcie_ep->perst_irq, IRQ_NOAUTOEN);
> >  	ret = devm_request_threaded_irq(&pdev->dev, pcie_ep->perst_irq, NULL,
> >  					qcom_pcie_ep_perst_irq_thread,
> >  					IRQF_TRIGGER_HIGH | IRQF_ONESHOT,
> > 
> > -- 
> > 2.25.1
> > 
> 

-- 
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