linux-kernel - Re: [PATCH v6 2/4] PCI: dwc: Always cache the maximum link speed value in dw_pcie::max_link

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Message-ID: <20240904154944.w4bujfmhy5uhzkld@thinkpad>
Date: Wed, 4 Sep 2024 21:19:44 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Johan Hovold <johan@...nel.org>
Cc: Richard Zhu <hongxing.zhu@....com>,
	Lucas Stach <l.stach@...gutronix.de>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>,
	Jingoo Han <jingoohan1@...il.com>,
	Chuanhua Lei <lchuanhua@...linear.com>,
	Marek Vasut <marek.vasut+renesas@...il.com>,
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
	linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	imx@...ts.linux.dev, linux-kernel@...r.kernel.org,
	linux-renesas-soc@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	abel.vesa@...aro.org, johan+linaro@...nel.org,
	Shashank Babu Chinta Venkata <quic_schintav@...cinc.com>
Subject: Re: [PATCH v6 2/4] PCI: dwc: Always cache the maximum link speed
 value in dw_pcie::max_link_speed

On Wed, Sep 04, 2024 at 11:30:08AM +0200, Johan Hovold wrote:
> On Wed, Sep 04, 2024 at 12:41:58PM +0530, Manivannan Sadhasivam via B4 Relay wrote:
> > From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> > 
> > Currently, dw_pcie::max_link_speed has a valid value only if the controller
> > driver restricts the maximum link speed in the driver or if the platform
> > does so in the devicetree using the 'max-link-speed' property.
> > 
> > But having the maximum supported link speed of the platform would be
> > helpful for the vendor drivers to configure any link specific settings.
> > So in the case of non-valid value in dw_pcie::max_link_speed, just cache
> > the hardware default value from Link Capability register.
> > 
> > While at it, let's also remove the 'max_link_speed' argument to the
> > dw_pcie_link_set_max_speed() function since the value can be retrieved
> > within the function.
> > 
> > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> > ---
> >  drivers/pci/controller/dwc/pcie-designware.c | 18 ++++++++++++++----
> >  1 file changed, 14 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
> > index 86c49ba097c6..0704853daa85 100644
> > --- a/drivers/pci/controller/dwc/pcie-designware.c
> > +++ b/drivers/pci/controller/dwc/pcie-designware.c
> > @@ -687,16 +687,27 @@ void dw_pcie_upconfig_setup(struct dw_pcie *pci)
> >  }
> >  EXPORT_SYMBOL_GPL(dw_pcie_upconfig_setup);
> >  
> > -static void dw_pcie_link_set_max_speed(struct dw_pcie *pci, u32 max_link_speed)
> > +static void dw_pcie_link_set_max_speed(struct dw_pcie *pci)
> >  {
> >  	u32 cap, ctrl2, link_speed;
> >  	u8 offset = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
> >  
> >  	cap = dw_pcie_readl_dbi(pci, offset + PCI_EXP_LNKCAP);
> > +
> > +	/*
> > +	 * Even if the platform doesn't want to limit the maximum link speed,
> > +	 * just cache the hardware default value so that the vendor drivers can
> > +	 * use it to do any link specific configuration.
> > +	 */
> > +	if (pci->max_link_speed < 0) {
> 
> This should be 
> 
> 	if (pci->max_link_speed < 1) {
> 

Well I was trying to catch the error value here because if neither driver nor
platform limits the max link speed, this would have -EINVAL (returned by
of_pci_get_max_link_speed()).

But logically it makes sense to use 'pci->max_link_speed < 1' since anything
below value 1 is an invalid value.

Will change it.

- Mani

> but the patch works as-is because of the default case in the switch
> below which falls back to PCI_EXP_LNKCAP_SLS.
> 
> > +		pci->max_link_speed = FIELD_GET(PCI_EXP_LNKCAP_SLS, cap);
> > +		return;
> > +	}
> > +
> >  	ctrl2 = dw_pcie_readl_dbi(pci, offset + PCI_EXP_LNKCTL2);
> >  	ctrl2 &= ~PCI_EXP_LNKCTL2_TLS;
> >  
> > -	switch (pcie_link_speed[max_link_speed]) {
> > +	switch (pcie_link_speed[pci->max_link_speed]) {
> >  	case PCIE_SPEED_2_5GT:
> >  		link_speed = PCI_EXP_LNKCTL2_TLS_2_5GT;
> >  		break;
> 
> > @@ -1058,8 +1069,7 @@ void dw_pcie_setup(struct dw_pcie *pci)
> >  {
> >  	u32 val;
> >  
> > -	if (pci->max_link_speed > 0)
> > -		dw_pcie_link_set_max_speed(pci, pci->max_link_speed);
> > +	dw_pcie_link_set_max_speed(pci);
> 
> With the above fixed:
> 
> Reviewed-by: Johan Hovold <johan+linaro@...nel.org>

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