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

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Message-ID: <azxdhgvf6vo6eilmdmxa2ryir33h5uqwuru2a7jrgjuunyncrb@q3fdjhcaskjm>
Date: Fri, 25 Apr 2025 21:16:09 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>, 
	Bjorn Helgaas <bhelgaas@...gle.com>, Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>, 
	Jingoo Han <jingoohan1@...il.com>, 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()

On Thu, Mar 13, 2025 at 12:00:01PM -0500, Bjorn Helgaas wrote:
> [+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?
> 

I'm not Bartosz, but I could speak for pwrctrl.

This should really be part of pci_pwrctrl_notify() in pwrctrl driver. Pwrctrl
driver is already getting notified with device additions and removals. So the
update can be performed once the device addition happens.

- Mani

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