linux-kernel - Re: [PATCH] PCI: qcom: Enable MSI interrupts together with Link up if global IRQ is supported

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Message-ID: <20241003045707.gy3zemtxrheuipr7@thinkpad>
Date: Thu, 3 Oct 2024 10:27:07 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: lpieralisi@...nel.org, kw@...ux.com, robh@...nel.org,
	bhelgaas@...gle.com, linux-pci@...r.kernel.org,
	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
	quic_qianyu@...cinc.com, Konrad Dybcio <konradybcio@...nel.org>
Subject: Re: [PATCH] PCI: qcom: Enable MSI interrupts together with Link up
 if global IRQ is supported

On Tue, Oct 01, 2024 at 04:19:57PM -0500, Bjorn Helgaas wrote:
> On Tue, Oct 01, 2024 at 09:50:55AM +0530, Manivannan Sadhasivam wrote:
> > On Mon, Sep 30, 2024 at 12:11:01PM -0500, Bjorn Helgaas wrote:
> > > On Mon, Sep 30, 2024 at 07:14:09PM +0530, Manivannan Sadhasivam wrote:
> > > > Currently, if global IRQ is supported by the platform, only the Link up
> > > > interrupt is enabled in the PARF_INT_ALL_MASK register. But on some Qcom
> > > > platforms like SM8250, and X1E80100, MSIs are getting masked due to this.
> > > > They require enabling the MSI interrupt bits in the register to unmask
> > > > (enable) the MSIs.
> > > 
> > > "global IRQ" is a very generic name.  If that's the official name, it
> > > should at least be capitalized, e.g., "Global IRQ", to show that it is
> > > a proper noun that refers to a specific IRQ.
> > 
> > Sure.
> > 
> > > > Even though the MSI interrupt enable bits in PARF_INT_ALL_MASK are
> > > > described as 'diagnostic' interrupts in the internal documentation,
> > > > disabling them masks MSI on these platforms. Due to this,
> > > 
> > > > MSIs were not
> > > > reported to be received these platforms while supporting global IRQ.
> > > 
> > > I'm trying to parse "while supporting global IRQ."  We basically
> > > support global IRQ by installing qcom_pcie_global_irq_thread(), but of
> > > course the device doesn't see that, so I assume it would be more
> > > informative to say that MSIs are masked by some register setting.
> > 
> > Hmm, this is what I mentioned in the above paragraph referencing
> > PARF_INT_ALL_MASK register. Is that not clear enough?
> 
> It requires the knowledge that the MSI enable bits are set by
> hardware, cleared by 4581403f6792, and set again here.  This will be
> more accessible to non-qcom experts if that information is included
> here.
> 

Okay.

> > > The patch suggests that MSIs are masked internally unless
> > > PARF_INT_MSI_DEV_0_7 is set in PARF_INT_ALL_MASK.
> > > 
> > > Are you saying that prior to 4581403f6792, MSIs did work?  Does that
> > > mean PARF_INT_MSI_DEV_0_7 was set by a bootloader or something, so
> > > MSIs worked?  And then 4581403f6792 came along and implicitly cleared
> > > PARF_INT_MSI_DEV_0_7, so MSIs were then masked?
> > 
> > Yeah. Those bits were enabled by default in hardware, but since they were
> > mentioned as 'diagnostic interrupts' in documentation, commit 4581403f6792
> > intentionally disabled them. But that results in MSIs getting masked in
> > *some* platforms.
> 
> Apparently the "*some* platforms" part is more qcom-expert knowledge?

I already mentioned those platforms in the commit message 'SM8250 and X1E80100'.

> There are other qcom platforms where MSIs are not disabled by
> 4581403f6792?  Information about which platforms are which also sounds
> useful for future maintenance.
> 

Yeah, SM8450 is the one which I know so far. I will mention it explicitly.

- Mani

> > > > So enable the MSI interrupts along with the Link up interrupt in the
> > > > PARF_INT_ALL_MASK register if global IRQ is supported. This ensures that
> > > > the MSIs continue to work and also the driver is able to catch the Link
> > > > up interrupt for enumerating endpoint devices.
> > > > 
> > > > Fixes: 4581403f6792 ("PCI: qcom: Enumerate endpoints based on Link up event in 'global_irq' interrupt")
> > > > Reported-by: Konrad Dybcio <konradybcio@...nel.org>
> > > > Closes: https://lore.kernel.org/linux-pci/9a692c98-eb0a-4d86-b642-ea655981ff53@kernel.org/
> > > > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> > > > ---
> > > >  drivers/pci/controller/dwc/pcie-qcom.c | 4 +++-
> > > >  1 file changed, 3 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> > > > index ef44a82be058..2b33d03ed054 100644
> > > > --- a/drivers/pci/controller/dwc/pcie-qcom.c
> > > > +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> > > > @@ -133,6 +133,7 @@
> > > >  
> > > >  /* PARF_INT_ALL_{STATUS/CLEAR/MASK} register fields */
> > > >  #define PARF_INT_ALL_LINK_UP			BIT(13)
> > > > +#define PARF_INT_MSI_DEV_0_7			GENMASK(30, 23)
> > > >  
> > > >  /* PARF_NO_SNOOP_OVERIDE register fields */
> > > >  #define WR_NO_SNOOP_OVERIDE_EN			BIT(1)
> > > > @@ -1716,7 +1717,8 @@ static int qcom_pcie_probe(struct platform_device *pdev)
> > > >  			goto err_host_deinit;
> > > >  		}
> > > >  
> > > > -		writel_relaxed(PARF_INT_ALL_LINK_UP, pcie->parf + PARF_INT_ALL_MASK);
> > > > +		writel_relaxed(PARF_INT_ALL_LINK_UP | PARF_INT_MSI_DEV_0_7,
> > > > +			       pcie->parf + PARF_INT_ALL_MASK);
> > > >  	}
> > > >  
> > > >  	qcom_pcie_icc_opp_update(pcie);
> > > > -- 
> > > > 2.25.1
> > > > 
> > 
> > -- 
> > மணிவண்ணன் சதாசிவம்

-- 
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