[PATCH v3] PCI: create revision file in sysfs
Daniel Vetter
daniel at ffwll.ch
Mon Nov 14 18:40:03 UTC 2016
On Fri, Nov 11, 2016 at 02:37:23PM +0000, Emil Velikov wrote:
> From: Emil Velikov <emil.velikov at collabora.com>
>
> Currently the revision isn't available via sysfs/libudev thus if one
> wants to know the value they need to read through the config file.
>
> This in itself wakes/powers up the device, causing unwanted delay
> since it can be quite costly.
>
> There are at least two userspace components which could make use the new
> file libpciaccess and libdrm. The former [used in various places] wakes
> up _every_ PCI device, which can be observed via glxinfo [when using
> Mesa 10.0+ drivers]. While the latter [in association with Mesa 13.0]
> can lead to 2-3 second delays while starting firefox, thunderbird or
> chromium.
>
> Expose the revision as a separate file, just like we do for the device,
> vendor, their subsystem version and class.
>
> Cc: Bjorn Helgaas <bhelgaas at google.com>
> Cc: linux-pci at vger.kernel.org
> Cc: Greg KH <gregkh at linuxfoundation.org>
> Link: https://bugs.freedesktop.org/show_bug.cgi?id=98502
> Tested-by: Mauro Santos <registo.mailling at gmail.com>
> Reviewed-by: Alex Deucher <alexander.deucher at amd.com>
> Signed-off-by: Emil Velikov <emil.velikov at collabora.com>
Given that waking a gpu can take somewhere between ages and forever, and
that we read the pci revisions everytime we launch a new gl app I think
this is the correct approach. Of course we could just patch libdrm and
everyone to not look at the pci revision, but that just leads to every
pci-based driver having a driver-private ioctl/getparam thing to expose
it. Which also doesn't make much sense.
Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
Björn, if you're all ok with this we'd like to start landing at least
libdrm patches before this patch hits a released kernel, just to shorten
the pain window for users waiting for upgrades.
Thanks, Daniel
> ---
> v2: Add r-b/t-b tags, slim down CC list, add note about userspace.
>
> v3: Add Documentation/ bits (Greg KH)
>
> Gents, please keep me in the CC list.
>
> Thanks
> Emil
> ---
> Documentation/ABI/testing/sysfs-bus-pci | 7 +++++++
> Documentation/filesystems/sysfs-pci.txt | 2 ++
> drivers/pci/pci-sysfs.c | 2 ++
> 3 files changed, 11 insertions(+)
>
> diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci
> index b3bc50f..5a1732b 100644
> --- a/Documentation/ABI/testing/sysfs-bus-pci
> +++ b/Documentation/ABI/testing/sysfs-bus-pci
> @@ -294,3 +294,10 @@ Description:
> a firmware bug to the system vendor. Writing to this file
> taints the kernel with TAINT_FIRMWARE_WORKAROUND, which
> reduces the supportability of your system.
> +
> +What: /sys/bus/pci/devices/.../revision
> +Date: November 2016
> +Contact: Emil Velikov <emil.l.velikov at gmail.com>
> +Description:
> + This file contains the revision field of the the PCI device.
> + The value comes from device config space. The file is read only.
> diff --git a/Documentation/filesystems/sysfs-pci.txt b/Documentation/filesystems/sysfs-pci.txt
> index 74eaac2..6ea1ced 100644
> --- a/Documentation/filesystems/sysfs-pci.txt
> +++ b/Documentation/filesystems/sysfs-pci.txt
> @@ -17,6 +17,7 @@ that support it. For example, a given bus might look like this:
> | |-- resource0
> | |-- resource1
> | |-- resource2
> + | |-- revision
> | |-- rom
> | |-- subsystem_device
> | |-- subsystem_vendor
> @@ -41,6 +42,7 @@ files, each with their own function.
> resource PCI resource host addresses (ascii, ro)
> resource0..N PCI resource N, if present (binary, mmap, rw[1])
> resource0_wc..N_wc PCI WC map resource N, if prefetchable (binary, mmap)
> + revision PCI revision (ascii, ro)
> rom PCI ROM resource, if present (binary, ro)
> subsystem_device PCI subsystem device (ascii, ro)
> subsystem_vendor PCI subsystem vendor (ascii, ro)
> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> index bcd10c7..0666287 100644
> --- a/drivers/pci/pci-sysfs.c
> +++ b/drivers/pci/pci-sysfs.c
> @@ -50,6 +50,7 @@ pci_config_attr(vendor, "0x%04x\n");
> pci_config_attr(device, "0x%04x\n");
> pci_config_attr(subsystem_vendor, "0x%04x\n");
> pci_config_attr(subsystem_device, "0x%04x\n");
> +pci_config_attr(revision, "0x%02x\n");
> pci_config_attr(class, "0x%06x\n");
> pci_config_attr(irq, "%u\n");
>
> @@ -568,6 +569,7 @@ static struct attribute *pci_dev_attrs[] = {
> &dev_attr_device.attr,
> &dev_attr_subsystem_vendor.attr,
> &dev_attr_subsystem_device.attr,
> + &dev_attr_revision.attr,
> &dev_attr_class.attr,
> &dev_attr_irq.attr,
> &dev_attr_local_cpus.attr,
> --
> 2.9.3
>
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--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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