linux-kernel - Re: [PATCH v2 01/10] PCI: update current bus speed as part of pci_bus_add

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Message-ID: <20250313170001.GA738398@bhelgaas>
Date: Thu, 13 Mar 2025 12:00:01 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>,
	Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
	Jingoo Han <jingoohan1@...il.com>,
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Rob Herring <robh@...nel.org>,
	Johannes Berg <johannes@...solutions.net>,
	Jeff Johnson <jjohnson@...nel.org>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	mhi@...ts.linux.dev, linux-wireless@...r.kernel.org,
	ath11k@...ts.infradead.org, quic_pyarlaga@...cinc.com,
	quic_vbadigan@...cinc.com, quic_vpernami@...cinc.com,
	quic_mrana@...cinc.com,
	Jeff Johnson <jeff.johnson@....qualcomm.com>,
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v2 01/10] PCI: update current bus speed as part of
 pci_bus_add_devices()

[+cc Bartosz since this is related to pwrctrl]

On Thu, Mar 13, 2025 at 05:10:08PM +0530, Krishna Chaitanya Chundru wrote:
> If the link is not up till the pwrctl drivers enable power to endpoints
> then cur_bus_speed will not be updated with correct speed.
> 
> As part of rescan, pci_bus_add_devices() will be called and as part of
> it update the link bus speed.
> 
> Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
> ---
>  drivers/pci/bus.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
> index 98910bc0fcc4..994879071d4c 100644
> --- a/drivers/pci/bus.c
> +++ b/drivers/pci/bus.c
> @@ -432,6 +432,9 @@ void pci_bus_add_devices(const struct pci_bus *bus)
>  	struct pci_dev *dev;
>  	struct pci_bus *child;
>  
> +	if (bus->self)
> +		pcie_update_link_speed((struct pci_bus *)bus);

Why the cast?  I guess to discard "const"?  I would prefer to avoid
that if we can.

The only existing callers of pcie_update_link_speed() are from bwctrl,
where it obviously makes sense because bwctrl manages link speed, and
from pci_set_bus_speed() in the pci_alloc_child_bus() path.

If we call pcie_update_link_speed() here, do we still need the
pci_set_bus_speed() in pci_alloc_child_bus()?

Bartosz, so you have any suggestions?  Is there a point in pwrctrl
where it would make sense to do this, similar to what bwctrl does?

>  	list_for_each_entry(dev, &bus->devices, bus_list) {
>  		/* Skip already-added devices */
>  		if (pci_dev_is_added(dev))
> 
> -- 
> 2.34.1
>