Re: [PATCH v4 04/11] PCI/ASPM: Use RMW accessors for changing LNKCTL

[Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>]

On Thu, Jul 13, 2023 at 03:44:58PM +0300, Ilpo Järvinen wrote:
> Don't assume that the device is fully under the control of ASPM and use
> RMW capability accessors which do proper locking to avoid losing
> concurrent updates to the register values.
> 
> If configuration fails in pcie_aspm_configure_common_clock(), the
> function attempts to restore the old PCI_EXP_LNKCTL_CCC settings. Store
> only the old PCI_EXP_LNKCTL_CCC bit for the relevant devices rather
> than the content of the whole LNKCTL registers. It aligns better with
> how pcie_lnkctl_clear_and_set() expects its parameter and makes the
> code more obvious to understand.

...

>  	int same_clock = 1;
> -	u16 reg16, parent_reg, child_reg[8];
> +	u16 reg16, parent_old_ccc, child_old_ccc[8];

	u16 ccc;

>  	struct pci_dev *child, *parent = link->pdev;
>  	struct pci_bus *linkbus = parent->subordinate;

...

	ccc = same_clock ? PCI_EXP_LNKCTL_CCC : 0);

>  	/* Configure downstream component, all functions */
>  	list_for_each_entry(child, &linkbus->devices, bus_list) {
>  		pcie_capability_read_word(child, PCI_EXP_LNKCTL, &reg16);
> -		child_reg[PCI_FUNC(child->devfn)] = reg16;
> -		if (same_clock)
> -			reg16 |= PCI_EXP_LNKCTL_CCC;
> -		else
> -			reg16 &= ~PCI_EXP_LNKCTL_CCC;
> -		pcie_capability_write_word(child, PCI_EXP_LNKCTL, reg16);
> +		child_old_ccc[PCI_FUNC(child->devfn)] = reg16 & PCI_EXP_LNKCTL_CCC;
> +		pcie_capability_clear_and_set_word(child, PCI_EXP_LNKCTL,
> +						   PCI_EXP_LNKCTL_CCC,
> +						   same_clock ? PCI_EXP_LNKCTL_CCC : 0);

		pcie_capability_clear_and_set_word(child, PCI_EXP_LNKCTL,
						   PCI_EXP_LNKCTL_CCC, ccc);

>  	}

...

> +	pcie_capability_clear_and_set_word(parent, PCI_EXP_LNKCTL,
> +					   PCI_EXP_LNKCTL_CCC,
> +					   same_clock ? PCI_EXP_LNKCTL_CCC : 0);

	pcie_capability_clear_and_set_word(parent, PCI_EXP_LNKCTL,
					   PCI_EXP_LNKCTL_CCC, ccc);

?

-- 
With Best Regards,
Andy Shevchenko