[PATCH] PCI/PME: Replace RMW of Root Status register with direct write

[PATCH] PCI/PME: Replace RMW of Root Status register with direct write

[Lukas Wunner]

As of PCIe r7.0, the Root Status register contains a single writeable bit
(PME Status, type RW1C) and otherwise just read-only bits and RsvdZ bits
(which software must write as zero, PCIe r7.0 sec 7.4).

Thus, when clearing the PME Status bit, there's no need to perform a
read-modify-write of the register.  Instead, the bit can be written
directly.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
---
 drivers/pci/pci.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index b14dd064006c..411a0b88841e 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -2285,7 +2285,7 @@ void pcie_clear_device_status(struct pci_dev *dev)
  */
 void pcie_clear_root_pme_status(struct pci_dev *dev)
 {
-	pcie_capability_set_dword(dev, PCI_EXP_RTSTA, PCI_EXP_RTSTA_PME);
+	pcie_capability_write_dword(dev, PCI_EXP_RTSTA, PCI_EXP_RTSTA_PME);
 }
 
 /**
-- 
2.51.0

Re: [PATCH] PCI/PME: Replace RMW of Root Status register with direct write

[Lukas Wunner]

On Sun, Oct 26, 2025 at 05:57:57PM +0100, Lukas Wunner wrote:
> As of PCIe r7.0, the Root Status register contains a single writeable bit
> (PME Status, type RW1C) and otherwise just read-only bits and RsvdZ bits
> (which software must write as zero, PCIe r7.0 sec 7.4).
> 
> Thus, when clearing the PME Status bit, there's no need to perform a
> read-modify-write of the register.  Instead, the bit can be written
> directly.

Hm, I just noticed that this patch is marked "Not Applicable" in patchwork:

https://patchwork.kernel.org/project/linux-pci/patch/39f87c99f6c44be3c0371c79e454e6fde7be0d4d.1761497583.git.lukas@wunner.de/

It didn't get any on-list replies and didn't get applied AFAICS.
I'm not sure why it's marked this way in patchwork or what to do about it.

There's one other patch sharing the same fate:

https://patchwork.kernel.org/project/linux-pci/patch/75e4ae507fa4faddd063a3a9e17d319ed84529b6.1757562971.git.lukas@wunner.de/

Thanks!

Lukas

Re: [PATCH] PCI/PME: Replace RMW of Root Status register with direct write

[Ilpo Järvinen]

[-- Attachment #1: Type: text/plain, Size: 1098 bytes --]

On Sun, 26 Oct 2025, Lukas Wunner wrote:

> As of PCIe r7.0, the Root Status register contains a single writeable bit
> (PME Status, type RW1C) and otherwise just read-only bits and RsvdZ bits
> (which software must write as zero, PCIe r7.0 sec 7.4).
> 
> Thus, when clearing the PME Status bit, there's no need to perform a
> read-modify-write of the register.  Instead, the bit can be written
> directly.
> 
> Signed-off-by: Lukas Wunner <lukas@wunner.de>
> ---
>  drivers/pci/pci.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index b14dd064006c..411a0b88841e 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -2285,7 +2285,7 @@ void pcie_clear_device_status(struct pci_dev *dev)
>   */
>  void pcie_clear_root_pme_status(struct pci_dev *dev)
>  {
> -	pcie_capability_set_dword(dev, PCI_EXP_RTSTA, PCI_EXP_RTSTA_PME);
> +	pcie_capability_write_dword(dev, PCI_EXP_RTSTA, PCI_EXP_RTSTA_PME);
>  }
>  
>  /**
> 

Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

-- 
 i.

Re: [PATCH] PCI/PME: Replace RMW of Root Status register with direct write

[Bjorn Helgaas]

On Sun, Oct 26, 2025 at 05:57:57PM +0100, Lukas Wunner wrote:
> As of PCIe r7.0, the Root Status register contains a single writeable bit
> (PME Status, type RW1C) and otherwise just read-only bits and RsvdZ bits
> (which software must write as zero, PCIe r7.0 sec 7.4).
> 
> Thus, when clearing the PME Status bit, there's no need to perform a
> read-modify-write of the register.  Instead, the bit can be written
> directly.
> 
> Signed-off-by: Lukas Wunner <lukas@wunner.de>

Applied to pci/enumeration for v6.20, thanks!

Thanks for the ping; I don't remember but suspect I just bulk-archived
old things in patchwork because it was so overwhelming.

> ---
>  drivers/pci/pci.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index b14dd064006c..411a0b88841e 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -2285,7 +2285,7 @@ void pcie_clear_device_status(struct pci_dev *dev)
>   */
>  void pcie_clear_root_pme_status(struct pci_dev *dev)
>  {
> -	pcie_capability_set_dword(dev, PCI_EXP_RTSTA, PCI_EXP_RTSTA_PME);
> +	pcie_capability_write_dword(dev, PCI_EXP_RTSTA, PCI_EXP_RTSTA_PME);
>  }
>  
>  /**
> -- 
> 2.51.0
>