On Wed, May 17, 2023 at 01:52:35PM +0300, Ilpo Järvinen wrote:
> Don't assume that only the driver would be accessing LNKCTL. ASPM
> policy changes can trigger write to LNKCTL outside of driver's control.
>
> Use RMW capability accessors which does proper locking to avoid losing
> concurrent updates to the register value. On restore, clear the ASPMC
> field properly.
>
> Fixes: 76d870ed09ab ("ath10k: enable ASPM")
> Suggested-by: Lukas Wunner <lukas@xxxxxxxxx>
> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> ---
> drivers/net/wireless/ath/ath10k/pci.c | 9 +++++----
> 1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/wireless/ath/ath10k/pci.c b/drivers/net/wireless/ath/ath10k/pci.c
> index a7f44f6335fb..9275a672f90c 100644
> --- a/drivers/net/wireless/ath/ath10k/pci.c
> +++ b/drivers/net/wireless/ath/ath10k/pci.c
> @@ -1963,8 +1963,9 @@ static int ath10k_pci_hif_start(struct ath10k *ar)
> ath10k_pci_irq_enable(ar);
> ath10k_pci_rx_post(ar);
>
> - pcie_capability_write_word(ar_pci->pdev, PCI_EXP_LNKCTL,
> - ar_pci->link_ctl);
> + pcie_capability_clear_and_set_word(ar_pci->pdev, PCI_EXP_LNKCTL,
> + PCI_EXP_LNKCTL_ASPMC,
> + ar_pci->link_ctl & PCI_EXP_LNKCTL_ASPMC);
>
> return 0;
> }
> @@ -2821,8 +2822,8 @@ static int ath10k_pci_hif_power_up(struct ath10k *ar,
>
> pcie_capability_read_word(ar_pci->pdev, PCI_EXP_LNKCTL,
> &ar_pci->link_ctl);
> - pcie_capability_write_word(ar_pci->pdev, PCI_EXP_LNKCTL,
> - ar_pci->link_ctl & ~PCI_EXP_LNKCTL_ASPMC);
> + pcie_capability_clear_word(ar_pci->pdev, PCI_EXP_LNKCTL,
> + PCI_EXP_LNKCTL_ASPMC);
These ath drivers all have the form:
1) read LNKCTL
2) save LNKCTL value in ->link_ctl
3) write LNKCTL with "->link_ctl & ~PCI_EXP_LNKCTL_ASPMC"
to disable ASPM
4) write LNKCTL with ->link_ctl, presumably to re-enable ASPM
These patches close the hole between 1) and 3) where other LNKCTL
updates could interfere, which is definitely a good thing.
But the hole between 1) and 4) is much bigger and still there. Any
update by the PCI core in that interval would be lost.
Straw-man proposal:
- Change pci_disable_link_state() so it ignores aspm_disabled and
always disables ASPM even if platform firmware hasn't granted
ownership. Maybe this should warn and taint the kernel.
- Change drivers to use pci_disable_link_state() instead of writing
LNKCTL directly.
Bjorn
