Re: [PATCH v2 2/2] PCI: sg2042: Avoid L0s and L1 on Sophgo 2042 PCIe Root Ports

[Manivannan Sadhasivam]

On Fri, Feb 27, 2026 at 06:19:25PM +0000, Yao Zi wrote:
> Since commit f3ac2ff14834 ("PCI/ASPM: Enable all ClockPM and ASPM
> states for devicetree platforms") force enable ASPM on all device tree
> platform, the SG2042 root port breaks as it advertises L0s and L1
> capabilities without supporting it.
> 
> Provide a platform-specific initialization hook to override the L0s and
> L1 support advertised in LNKCAP register of SG2042 Root Ports, so it
> doesn't try to enable those states.
> 
> Fixes: 4e27aca4881a ("riscv: sophgo: dts: add PCIe controllers for SG2042")
> Co-authored-by: Inochi Amaoto <inochiama@xxxxxxxxx>
> Signed-off-by: Inochi Amaoto <inochiama@xxxxxxxxx>
> Signed-off-by: Yao Zi <me@xxxxxxxx>
> ---
>  drivers/pci/controller/cadence/pcie-sg2042.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/drivers/pci/controller/cadence/pcie-sg2042.c b/drivers/pci/controller/cadence/pcie-sg2042.c
> index 0c50c74d03ee..3142f82bd393 100644
> --- a/drivers/pci/controller/cadence/pcie-sg2042.c
> +++ b/drivers/pci/controller/cadence/pcie-sg2042.c
> @@ -32,6 +32,25 @@ static struct pci_ops sg2042_pcie_child_ops = {
>  	.write		= pci_generic_config_write,
>  };
>  
> +static int sg2042_pcie_disable_l0s_l1(struct cdns_pcie_rc *rc)
> +{
> +	struct cdns_pcie *pcie = &rc->pcie;
> +	u32 pcie_lnkcap_off;
> +	u32 lnkcap;
> +
> +	pcie_lnkcap_off = CDNS_PCIE_RP_CAP_OFFSET + PCI_EXP_LNKCAP;
> +
> +	lnkcap = cdns_pcie_rp_readw(pcie, pcie_lnkcap_off);
> +	lnkcap &= ~PCI_EXP_LNKCAP_ASPMS;
> +	cdns_pcie_rp_writew(pcie, pcie_lnkcap_off, lnkcap);
> +

cadence-host driver already has cdns_pcie_host_init_root_port() to initialize
the Root Port. Since your intention is to modify the LNKCAP field, which belongs
to the Root Port, you should do that in cdns_pcie_host_init_root_port() instead.
I see no sg2042 specific registers used in this patch, so just set a flag in
this driver like 'broken_aspm' and clear PCI_EXP_LNKCAP_ASPMS if set in
cdns_pcie_host_init_root_port().

- Mani

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