RE: [v2] PCI: imx: make msi work without pcieportbus

[Richard Zhu <hongxing.zhu@nxp.com>]

Hi Bjorn:
Thanks for your kindly review.

> -----Original Message-----
> From: Bjorn Helgaas [mailto:helgaas@kernel.org]
> Sent: 2018年12月13日 22:41
> To: Richard Zhu <hongxing.zhu@nxp.com>
> Cc: lorenzo.pieralisi@arm.com; l.stach@pengutronix.de;
> andrew.smirnov@gmail.com; linux-pci@vger.kernel.org;
> linux-kernel@vger.kernel.org; linux-arm-kernel@lists.infradead.org
> Subject: Re: [v2] PCI: imx: make msi work without pcieportbus
> 
> On Thu, Dec 13, 2018 at 08:02:11AM +0000, Richard Zhu wrote:
> > MSI_EN of iMX PCIe RC would be asserted when PCIEPORTBUS driver is
> > selected.
> > Thus, the MSI works fine on iMX PCIe before.
> > Assert it unconditionally when MSI is supported.
> > Otherwise, the MSI wouldn't be triggered although the EP is present
> > and the MSIs are assigned.
> 
> This subject line and changelog need some rework.  I can't understand
> what's going on at all.  Lorenzo or I can help craft something, but I don't
> understand enough to propose anything yet.
> 
> "MSI_EN" doesn't appear in the driver; I assume it's some device-specific
> signal.
[Richard Zhu] MSI_EN is the MSI Enable bit(BIT(0)) of the Message Control Register for MSI.
I would change it to MSI Enable bit later.

> 
> "iMX" does not look like the typical spelling.  You could use "imx6"
> to refer to the driver, but in this case you're talking about the hardware itself,
> not the driver.  So you should use "i.MX6" or whatever the appropriate brand
> is.
[Richard Zhu] Okay, i.MX6 would be used.
> 
> If "PCIEPORTBUS driver is selected" means "CONFIG_PCIEPORTBUS=y", say
> that.  The connection of portdrv (which is generic PCIe support) to MSI_EN
> (which is apparently device-specific) is unclear.  It would be helpful if you
> could connect those dots a little more.
[Richard Zhu] That's right, thanks.
> 
> "MSI works fine on iMX PCIe before."  Before what?  Is this a regression,
> where MSI worked before some commit and this patch fixes it?
[Richard Zhu] MSI works fine on iMX6 PCIe before commit "f3fdfc4ac3".
It's a limitation of the iMX6 PCIe, otherwise a regression. MSI should not
 have dependency on the selection of the PCIEPORTBUS
> 
> Please rewrap the changelog so it uses the entire 80-column width.
> Wrap to 75 so it still fits when "git log" adds the 4 char indent.
> 
[Richard Zhu] Okay.

> > Signed-off-by: Richard Zhu <hongxing.zhu@nxp.com>
> > ---
> >  drivers/pci/controller/dwc/pci-imx6.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> >
> > diff --git a/drivers/pci/controller/dwc/pci-imx6.c
> > b/drivers/pci/controller/dwc/pci-imx6.c
> > index 26087b3..d3e4296 100644
> > --- a/drivers/pci/controller/dwc/pci-imx6.c
> > +++ b/drivers/pci/controller/dwc/pci-imx6.c
> > @@ -74,6 +74,7 @@ struct imx6_pcie {
> >  #define PHY_PLL_LOCK_WAIT_USLEEP_MAX	200
> >
> >  /* PCIe Root Complex registers (memory-mapped) */
> > +#define PCI_MSI_CAP				0x50
> 
> I wish this didn't look quite so much like a PCI core name, because this is
> really an i.MX-specific offset.  It looks like the PCIE_RC_* names are all
> similar i.MX-specific things.  Shouldn't this match those?
> 
[Richard Zhu] How about to replace it by PCIE_RC_IMX6_MSI_CAP?

Best Regards
Richard Zhu

> >  #define PCIE_RC_LCR				0x7c
> >  #define PCIE_RC_LCR_MAX_LINK_SPEEDS_GEN1	0x1
> >  #define PCIE_RC_LCR_MAX_LINK_SPEEDS_GEN2	0x2
> > @@ -926,6 +927,7 @@ static int imx6_pcie_probe(struct platform_device
> *pdev)
> >  	struct resource *dbi_base;
> >  	struct device_node *node = dev->of_node;
> >  	int ret;
> > +	u16 val;
> >
> >  	imx6_pcie = devm_kzalloc(dev, sizeof(*imx6_pcie), GFP_KERNEL);
> >  	if (!imx6_pcie)
> > @@ -1070,6 +1072,11 @@ static int imx6_pcie_probe(struct
> platform_device *pdev)
> >  	ret = imx6_add_pcie_port(imx6_pcie, pdev);
> >  	if (ret < 0)
> >  		return ret;
> > +	if (IS_ENABLED(CONFIG_PCI_MSI)) {
> > +		val = dw_pcie_readw_dbi(pci, PCI_MSI_CAP + PCI_MSI_FLAGS);
> > +		val |= PCI_MSI_FLAGS_ENABLE;
> > +		dw_pcie_writew_dbi(pci, PCI_MSI_CAP + PCI_MSI_FLAGS, val);
> > +	}
> >
> >  	return 0;
> >  }
> > --
> > 2.7.4
> >
> >
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