Re: [PATCH v6 2/3] PCI/ASPM: Disable/restore ASPM on every function for multi-function devices

On Mon, Jul 27, 2026 at 07:32:37PM +0530, Krishna Chaitanya Chundru wrote:
> pcie_aspm_cap_init() disables ASPM L0s/L1 before touching L1SS config,
> then restores the pre-existing state afterward. Both steps only ever
> touched link->downstream, i.e. function 0 of the downstream component,
> leaving sibling functions (>0) on a multi-function device untouched.
> 
> This means the "disable" step does not actually disable ASPM link-wide
> on a multi-function device: a sibling function can still have L1
> enabled even after this step runs. PCIe r6.2 sec 7.5.3.7 recommends
> programming the same ASPM Control value for all functions of a
> multi-function device, and pcie_config_aspm_link() already loops over
> every function on the bus for exactly this reason.
> 
> Loop over every function on linkbus->devices for both the disable and
> restore steps, keeping the existing PCIe r6.2 sec 7.5.3.7 ordering
> (disable downstream functions before upstream, restore upstream before
> downstream functions). The masked pcie_capability_clear_and_set_word()
> accessor from the previous commit makes this safe: it only ever
> touches the ASPM Control bits, so function-specific bits elsewhere in
> LNKCTL (e.g. Read Completion Boundary, CLKREQ Enable) on sibling
> functions are left untouched.
> 
> Fixes: 7447990137bf ("PCI/ASPM: Disable L1 before disabling L1 PM Substates")

Reported-by: Sashiko <[email protected]>
Closes: https://lore.kernel.org/all/[email protected]/

> Signed-off-by: Krishna Chaitanya Chundru <[email protected]>

Reviewed-by: Manivannan Sadhasivam <[email protected]>

- Mani

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