linux-kernel - Re: [PATCH 1/1] PCI/bwctrl: Replace lbms_count with PCIE_LINK_LBMS

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Message-ID: <aAELZfjCCZUE4aos@wunner.de>
Date: Thu, 17 Apr 2025 16:08:37 +0200
From: Lukas Wunner <lukas@...ner.de>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] PCI/bwctrl: Replace lbms_count with
 PCIE_LINK_LBMS_SEEN flag

On Thu, Apr 17, 2025 at 03:46:32PM +0300, Ilpo Järvinen wrote:
> PCIe BW controller counts LBMS assertions for the purposes of the
> Target Speed quirk. It was also a plan to expose the LBMS count through
> sysfs to allow better diagnosing link related issues. Lukas Wunner
> suggested, however, that adding a trace event would be better for
> diagnostics purposes. Leaving only Target Speed quirk as an user of the
> lbms_count.
> 
> The logic in the Target Speed quirk does not require keeping count of
> LBMS assertions but a simple flag is enough which can be placed into
> pci_dev's priv_flags. The reduced complexity allows removing
> pcie_bwctrl_lbms_rwsem.
[...]
> This will conflict with the new flags Lukas added due to the hp fixes
> but it should be simple to deal with that conflict while merging the
> topic branches.

Hm, perhaps it would be easier to merge this if it would use bit 6
instead of bit 4.  Then it would just be a trivial merge conflict
between two topic branches (pci/hotplug and pci/bwctrl, I presume).
The way it is now, it will require manually tweaking the bit after
applying the patch.

> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -557,6 +557,7 @@ static inline int pci_dev_set_disconnected(struct pci_dev *dev, void *unused)
>  #define PCI_DPC_RECOVERED 1
>  #define PCI_DPC_RECOVERING 2
>  #define PCI_DEV_REMOVED 3
> +#define PCIE_LINK_LBMS_SEEN	4

The two newly added bits on the pci/hotplug branch use the prefix
"PCI_LINK_".  It would be slightly neater if this used the same prefix.

>  drivers/pci/hotplug/pciehp_ctrl.c |  2 +-
>  drivers/pci/pci.c                 |  2 +-
>  drivers/pci/pci.h                 | 10 ++---
>  drivers/pci/pcie/bwctrl.c         | 63 +++++++++----------------------
>  drivers/pci/quirks.c              | 10 ++---
>  5 files changed, 25 insertions(+), 62 deletions(-)

Obviously a nice, welcome simplification, shaving off 37 LoC.
Thanks for doing this!

Lukas