[PATCH 1/1] PCI/bwctrl: Fix link speed return type

[PATCH 1/1] PCI/bwctrl: Fix link speed return type

[Ilpo Järvinen]

pcie_bwctrl_select_speed() should take __fls() of the speed bit, not
return it as a raw value. Instead of directly returning 2.5GT/s speed
bit, simply assign the fallback speed (2.5GT/s) into supported_speeds
variable to share the normal return path that calls
pcie_supported_speeds2target_speed() to calculate __fls().

This code path is not very likely to execute because
pcie_get_supported_speeds() should provide valid ->supported_speeds but
a spec violating device could fail to synthetize any speed in
pcie_get_supported_speeds(). It could also happen in case the
supported_speeds intersection is empty (also a violation of the current
PCIe specs).

Fixes: de9a6c8d5dbf ("PCI/bwctrl: Add pcie_set_target_speed() to set PCIe Link Speed")
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
---
 drivers/pci/pcie/bwctrl.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pci/pcie/bwctrl.c b/drivers/pci/pcie/bwctrl.c
index 0a5e7efbce2c..58ba8142c9a3 100644
--- a/drivers/pci/pcie/bwctrl.c
+++ b/drivers/pci/pcie/bwctrl.c
@@ -113,7 +113,7 @@ static u16 pcie_bwctrl_select_speed(struct pci_dev *port, enum pci_bus_speed spe
 		up_read(&pci_bus_sem);
 	}
 	if (!supported_speeds)
-		return PCI_EXP_LNKCAP2_SLS_2_5GB;
+		supported_speeds = PCI_EXP_LNKCAP2_SLS_2_5GB;
 
 	return pcie_supported_speeds2target_speed(supported_speeds & desired_speeds);
 }

base-commit: 2014c95afecee3e76ca4a56956a936e23283f05b
-- 
2.39.5

Re: [PATCH 1/1] PCI/bwctrl: Fix link speed return type

[Bjorn Helgaas]

On Fri, Mar 21, 2025 at 06:31:03PM +0200, Ilpo Järvinen wrote:
> pcie_bwctrl_select_speed() should take __fls() of the speed bit, not
> return it as a raw value. Instead of directly returning 2.5GT/s speed
> bit, simply assign the fallback speed (2.5GT/s) into supported_speeds
> variable to share the normal return path that calls
> pcie_supported_speeds2target_speed() to calculate __fls().
> 
> This code path is not very likely to execute because
> pcie_get_supported_speeds() should provide valid ->supported_speeds but
> a spec violating device could fail to synthetize any speed in
> pcie_get_supported_speeds(). It could also happen in case the
> supported_speeds intersection is empty (also a violation of the current
> PCIe specs).
> 
> Fixes: de9a6c8d5dbf ("PCI/bwctrl: Add pcie_set_target_speed() to set PCIe Link Speed")
> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

Applied to pci/bwctrl for v6.15, thanks!

> ---
>  drivers/pci/pcie/bwctrl.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/pcie/bwctrl.c b/drivers/pci/pcie/bwctrl.c
> index 0a5e7efbce2c..58ba8142c9a3 100644
> --- a/drivers/pci/pcie/bwctrl.c
> +++ b/drivers/pci/pcie/bwctrl.c
> @@ -113,7 +113,7 @@ static u16 pcie_bwctrl_select_speed(struct pci_dev *port, enum pci_bus_speed spe
>  		up_read(&pci_bus_sem);
>  	}
>  	if (!supported_speeds)
> -		return PCI_EXP_LNKCAP2_SLS_2_5GB;
> +		supported_speeds = PCI_EXP_LNKCAP2_SLS_2_5GB;
>  
>  	return pcie_supported_speeds2target_speed(supported_speeds & desired_speeds);
>  }
> 
> base-commit: 2014c95afecee3e76ca4a56956a936e23283f05b
> -- 
> 2.39.5
>