Re: [PATCH v5 1/6] PCI/TPH: Fix pcie_tph_get_st_table_loc() field extraction

[Alex Williamson <alex.williamson@nvidia.com>]

On Mon, 27 Apr 2026 16:58:38 +0800
Chengwen Feng <fengchengwen@huawei.com> wrote:

> pcie_tph_get_st_table_loc() incorrectly uses FIELD_GET(), which shifts the
> field value to bit 0. But the function is designed to return raw
> PCI_TPH_LOC_* values as defined in the function comment.
> 
> This causes incorrect ST table location detection. Fix it by using bitwise
> AND with PCI_TPH_CAP_LOC_MASK to return the unshifted field value matching
> the function specification.
> 
> Fixes: d2e8a34876ce ("PCI/TPH: Add Steering Tag support")
> Cc: stable@vger.kernel.org
> Signed-off-by: Chengwen Feng <fengchengwen@huawei.com>
> ---
>  drivers/pci/tph.c | 8 +-------
>  1 file changed, 1 insertion(+), 7 deletions(-)

AFAICT, this is effectively a no-op within drivers/pci/tph.c.  We remove
the FIELD_GET(), but we also remove the FIELD_PREP(), so the end result
is no change, other than to align with the function comment.

However, not mentioned in the commit log, mlx5_st_create() expects the
documented rather than implemented behavior here.  That should be noted
here to justify the Fixes: tag.

Reviewed-by: Alex Williamson <alex.williamson@nvidia.com>

Nit below...
 
> diff --git a/drivers/pci/tph.c b/drivers/pci/tph.c
> index 91145e8d9d95..f17b74b5fb1e 100644
> --- a/drivers/pci/tph.c
> +++ b/drivers/pci/tph.c
> @@ -170,7 +170,7 @@ u32 pcie_tph_get_st_table_loc(struct pci_dev *pdev)
>  
>  	pci_read_config_dword(pdev, pdev->tph_cap + PCI_TPH_CAP, &reg);
>  
> -	return FIELD_GET(PCI_TPH_CAP_LOC_MASK, reg);
> +	return reg & PCI_TPH_CAP_LOC_MASK;
>  }
>  EXPORT_SYMBOL(pcie_tph_get_st_table_loc);
>  
> @@ -183,11 +183,7 @@ u16 pcie_tph_get_st_table_size(struct pci_dev *pdev)
>  	u32 reg;
>  	u32 loc;
>  
> -	/* Check ST table location first */

This comment still seems valid.  Thanks,

Alex

>  	loc = pcie_tph_get_st_table_loc(pdev);
> -
> -	/* Convert loc to match with PCI_TPH_LOC_* defined in pci_regs.h */
> -	loc = FIELD_PREP(PCI_TPH_CAP_LOC_MASK, loc);
>  	if (loc != PCI_TPH_LOC_CAP)
>  		return 0;
>  
> @@ -316,8 +312,6 @@ int pcie_tph_set_st_entry(struct pci_dev *pdev, unsigned int index, u16 tag)
>  	set_ctrl_reg_req_en(pdev, PCI_TPH_REQ_DISABLE);
>  
>  	loc = pcie_tph_get_st_table_loc(pdev);
> -	/* Convert loc to match with PCI_TPH_LOC_* */
> -	loc = FIELD_PREP(PCI_TPH_CAP_LOC_MASK, loc);
>  
>  	switch (loc) {
>  	case PCI_TPH_LOC_MSIX: