Re: [PATCH] PCI: dw-rockchip: Remove PCIE_L0S_ENTRY check from rockchip_pcie_link_up()

[Niklas Cassel <cassel@kernel.org>]

Hello Mani,

On Sun, Apr 13, 2025 at 07:54:28PM +0530, Manivannan Sadhasivam wrote:
> On Wed, Apr 09, 2025 at 11:19:03AM +0200, Niklas Cassel wrote:
> > 
> > It seems like we should really add a warning and a comment in
> > dw_pcie_link_up(), so that others don't get hit by this hard to debug issue!
> > 
> 
> Right. But I'm also wondering if we should use the 'Data Link Layer Link Active'
> bit in PCI Express Capability for checking link up. Qcom driver has been using
> it from the start and there are no reported issues. We could add this as the
> first fallback if the link_up callback is not provided.

Sounds like a good idea, but from looking at:
7.5.3.6 Link Capabilities Register (Offset 0Ch)

"
Data Link Layer Link Active Reporting Capable - For a Downstream Port,
this bit must be hardwired to 1b if the component supports the optional
capability of reporting the DL_Active state of the Data Link Control and
Management State Machine. For a hot-plug capable Downstream Port (as
indicated by the Hot-Plug Capable bit of the Slot Capabilities Register)
or a Downstream Port that supports Link speeds greater than 5.0 GT/s,
this bit must be hardwired to 1b.

For Upstream Ports and components that do not support this optional
capability, this bit must be hardwired to 0b.
"

It sounds like the the 'Data Link Layer Link Active' bit is optional,
or at least optional for Gen1 and Gen2.


Kind regards,
Niklas