linux-kernel - Re: [PATCH v3 1/3] PCI/MSI: Move MSI/MSI-X init to msi.c

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Message-ID: <X8oX61zRwV7ykLAy@ulmo>
Date:   Fri, 4 Dec 2020 12:05:15 +0100
From:   Thierry Reding <thierry.reding@...il.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Vidya Sagar <vidyas@...dia.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Krishna Kishore <kthota@...dia.com>,
        Manikanta Maddireddy <mmaddireddy@...dia.com>,
        Vidya Sagar <sagar.tv@...il.com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH v3 1/3] PCI/MSI: Move MSI/MSI-X init to msi.c

On Thu, Dec 03, 2020 at 12:51:08PM -0600, Bjorn Helgaas wrote:
> From: Bjorn Helgaas <bhelgaas@...gle.com>
> 
> Move pci_msi_setup_pci_dev(), which disables MSI and MSI-X interrupts, from
> probe.c to msi.c so it's with all the other MSI code and more consistent
> with other capability initialization.  This means we must compile msi.c
> always, even without CONFIG_PCI_MSI, so wrap the rest of msi.c in an #ifdef
> and adjust the Makefile accordingly.  No functional change intended.
> 
> Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
> ---
>  drivers/pci/Makefile |  3 +--
>  drivers/pci/msi.c    | 36 ++++++++++++++++++++++++++++++++++++
>  drivers/pci/pci.h    |  2 ++
>  drivers/pci/probe.c  | 21 ++-------------------
>  4 files changed, 41 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/pci/Makefile b/drivers/pci/Makefile
> index 522d2b974e91..11cc79411e2d 100644
> --- a/drivers/pci/Makefile
> +++ b/drivers/pci/Makefile
> @@ -5,7 +5,7 @@
>  obj-$(CONFIG_PCI)		+= access.o bus.o probe.o host-bridge.o \
>  				   remove.o pci.o pci-driver.o search.o \
>  				   pci-sysfs.o rom.o setup-res.o irq.o vpd.o \
> -				   setup-bus.o vc.o mmap.o setup-irq.o
> +				   setup-bus.o vc.o mmap.o setup-irq.o msi.o
>  
>  obj-$(CONFIG_PCI)		+= pcie/
>  
> @@ -18,7 +18,6 @@ endif
>  obj-$(CONFIG_OF)		+= of.o
>  obj-$(CONFIG_PCI_QUIRKS)	+= quirks.o
>  obj-$(CONFIG_HOTPLUG_PCI)	+= hotplug/
> -obj-$(CONFIG_PCI_MSI)		+= msi.o
>  obj-$(CONFIG_PCI_ATS)		+= ats.o
>  obj-$(CONFIG_PCI_IOV)		+= iov.o
>  obj-$(CONFIG_PCI_BRIDGE_EMUL)	+= pci-bridge-emul.o
> diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
> index d52d118979a6..555791c0ee1a 100644
> --- a/drivers/pci/msi.c
> +++ b/drivers/pci/msi.c
> @@ -26,6 +26,8 @@
>  
>  #include "pci.h"
>  
> +#ifdef CONFIG_MSI
> +
>  static int pci_msi_enable = 1;
>  int pci_msi_ignore_mask;
>  
> @@ -1577,3 +1579,37 @@ bool pci_dev_has_special_msi_domain(struct pci_dev *pdev)
>  }
>  
>  #endif /* CONFIG_PCI_MSI_IRQ_DOMAIN */
> +#endif /* CONFIG_PCI_MSI */
> +
> +void pci_msi_init(struct pci_dev *dev)
> +{
> +	u16 ctrl;
> +
> +	/*
> +	 * Disable the MSI hardware to avoid screaming interrupts
> +	 * during boot.  This is the power on reset default so
> +	 * usually this should be a noop.
> +	 */
> +	dev->msi_cap = pci_find_capability(dev, PCI_CAP_ID_MSI);
> +	if (!dev->msi_cap)
> +		return;
> +
> +	pci_read_config_word(dev, dev->msi_cap + PCI_MSI_FLAGS, &ctrl);
> +	if (ctrl & PCI_MSI_FLAGS_ENABLE)
> +		pci_write_config_word(dev, dev->msi_cap + PCI_MSI_FLAGS,
> +				      ctrl & ~PCI_MSI_FLAGS_ENABLE);
> +}

The old code used the pci_msi_set_enable() helper here...

> +
> +void pci_msix_init(struct pci_dev *dev)
> +{
> +	u16 ctrl;
> +
> +	dev->msix_cap = pci_find_capability(dev, PCI_CAP_ID_MSIX);
> +	if (!dev->msix_cap)
> +		return;
> +
> +	pci_read_config_word(dev, dev->msix_cap + PCI_MSIX_FLAGS, &ctrl);
> +	if (ctrl & PCI_MSIX_FLAGS_ENABLE)
> +		pci_write_config_word(dev, dev->msix_cap + PCI_MSIX_FLAGS,
> +				      ctrl & ~PCI_MSIX_FLAGS_ENABLE);
> +}

... and pci_msix_clear_and_set_ctrl() here. I like your version here
better because it avoids the unnecessary write in case the flag isn't
set. But it got me thinking if perhaps the helpers aren't very useful
and perhaps should be dropped in favour of open-coded variants.
Especially since there seem to be only 4 and 6 occurrences of them after
this patch.

Anyway, this patch looks correct to me and is a nice improvement, so:

Reviewed-by: Thierry Reding <treding@...dia.com>

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