linux-kernel - Re: [PATCH v2 1/2] PCI: dwc: Add host_post

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Date:   Mon, 16 Oct 2023 15:58:49 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc:     lpieralisi@...nel.org, kw@...ux.com, bhelgaas@...gle.com,
        robh@...nel.org, gustavo.pimentel@...opsys.com,
        jingoohan1@...il.com, andersson@...nel.org,
        konrad.dybcio@...aro.org, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v2 1/2] PCI: dwc: Add host_post_init() callback

On Tue, Oct 10, 2023 at 09:29:13PM +0530, Manivannan Sadhasivam wrote:
> This callback can be used by the platform drivers to do configuration once
> all the devices are scanned. Like changing LNKCTL of all downstream devices
> to enable ASPM etc...
> 
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> ---
>  drivers/pci/controller/dwc/pcie-designware-host.c | 3 +++
>  drivers/pci/controller/dwc/pcie-designware.h      | 1 +
>  2 files changed, 4 insertions(+)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> index a7170fd0e847..7991f0e179b2 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> @@ -502,6 +502,9 @@ int dw_pcie_host_init(struct dw_pcie_rp *pp)
>  	if (ret)
>  		goto err_stop_link;
>  
> +	if (pp->ops->host_post_init)
> +		pp->ops->host_post_init(pp);

I know we talked about this a little bit in the context of enabling
ASPM for devices below qcom 1.9.0 controllers at
https://lore.kernel.org/r/20231011050058.GC3508@thinkpad

But I didn't realize at the time that this callback adds a fundamental
difference between devices present at boot-time (these devices can be
affected by this callback) and any devices hot-added later (we never
run this callback again, so anything done by .host_post_init() never
applies to them).

We merged this for now, and it helps enable ASPM for builtin devices
on qcom, but I don't feel good about this from a larger DWC
perspective.  If other drivers use this and they support hot-add, I
think we're going to have problems.

>  	return 0;
>  
>  err_stop_link:
> diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
> index ef0b2efa9f93..efb4d4754fc8 100644
> --- a/drivers/pci/controller/dwc/pcie-designware.h
> +++ b/drivers/pci/controller/dwc/pcie-designware.h
> @@ -301,6 +301,7 @@ enum dw_pcie_ltssm {
>  struct dw_pcie_host_ops {
>  	int (*host_init)(struct dw_pcie_rp *pp);
>  	void (*host_deinit)(struct dw_pcie_rp *pp);
> +	void (*host_post_init)(struct dw_pcie_rp *pp);
>  	int (*msi_host_init)(struct dw_pcie_rp *pp);
>  	void (*pme_turn_off)(struct dw_pcie_rp *pp);
>  };
> -- 
> 2.25.1
>