Note subject line convention for drivers/pci (use "git log --oneline
drivers/pci/pci-sysfs.c")
On Wed, Jun 26, 2024 at 01:43:30PM +0900, Kobayashi,Daisuke wrote:
> This proposal aims to add a feature that outputs PCIe device power
> consumption information to sysfs.
>
> This feature can be implemented by adding support for PBEC (Power
> Budgeting Extended Capability) output to the PCIe driver. PBEC is
> defined in the PCIe specification(7.8.1) and is a standard method for
> obtaining device power consumption information.
s/This feature can be implemented by adding support/Add support/
(To change this to imperative mood and say what the patch actually
*does*, as opposed to what *could* be done.)
Include spec revision, e.g., "PCIe r6.0, sec 7.8.1"
> PCIe devices can significantly impact the overall power consumption of
> a system. However, obtaining PCIe device power consumption information
> has traditionally been difficult. This is because the 'lspci' command,
> which is a standard tool for displaying information about PCI devices,
> cannot access PBEC information. `lspci` is a standard tool for displaying
> information about PCI devices.
lspci detail isn't really necessary here. Maybe lspci *could* be
extended to display PBEC information, but that's a separate project.
It looks like the Data/Data Select issue might mean lspci would have
to get the info from the kernel, e.g., from this sysfs file, to avoid
synchronization issues.
> The PBEC Data register changes depending on the value of the PBEC Data
> Select register. To obtain all PBEC Data register values defined in the
> device, obtain the value of the PBEC Data register while changing the
> value of the PBEC Data Select register.
>
> Signed-off-by: "Kobayashi,Daisuke" <kobayashi.da-06@xxxxxxxxxxx>
> ---
> drivers/pci/pci-sysfs.c | 28 ++++++++++++++++++++++++++++
> 1 file changed, 28 insertions(+)
>
> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> index 2321fdfefd7d..b13d30da38a1 100644
> --- a/drivers/pci/pci-sysfs.c
> +++ b/drivers/pci/pci-sysfs.c
> @@ -182,6 +182,33 @@ static ssize_t resource_show(struct device *dev, struct device_attribute *attr,
> }
> static DEVICE_ATTR_RO(resource);
>
> +static ssize_t pbec_show(struct device *dev, struct device_attribute *attr,
> + char *buf)
> +{
> + struct pci_dev *pci_dev = to_pci_dev(dev);
> + size_t len = 0;
> + int i, pos;
> + u32 data;
> +
> + if (!pci_is_pcie(pci_dev))
> + return 0;
Unnecessary. Already covered by pcie_dev_attrs_are_visible().
> + pos = pci_find_ext_capability(pci_dev, PCI_EXT_CAP_ID_PWR);
> + if (!pos)
> + return 0;
> +
> + for (i = 0; i < 0xff; i++) {
> + pci_write_config_byte(pci_dev, pos + PCI_PWR_DSR, (u8)i);
> + pci_read_config_dword(pci_dev, pos + PCI_PWR_DATA, &data);
> + if (!data)
> + break;
> + len += sysfs_emit_at(buf, len, "%04x\n", data);
> + }
> +
> + return len;
> +}
> +static DEVICE_ATTR_RO(pbec);
Needs a more descriptive name, I think. Also some documentation in
Documentation/ABI/.
> static ssize_t max_link_speed_show(struct device *dev,
> struct device_attribute *attr, char *buf)
> {
> @@ -629,6 +656,7 @@ static struct attribute *pcie_dev_attrs[] = {
> &dev_attr_current_link_width.attr,
> &dev_attr_max_link_width.attr,
> &dev_attr_max_link_speed.attr,
> + &dev_attr_pbec.attr,
> NULL,
> };
>
> --
> 2.44.0
>
