Re: [PATCH v3 1/3] PCI: j721e: Add PCIe 4x lane selection support

[Vignesh Raghavendra <vigneshr@ti.com>]

Hi Matt,

On 20/10/22 6:59 am, Matt Ranostay wrote:
> Add support for setting of two-bit field that allows selection of 4x
> lane PCIe which was previously limited to only 2x lanes.
> 
> Signed-off-by: Matt Ranostay <mranostay@ti.com>
> ---
>  drivers/pci/controller/cadence/pci-j721e.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/controller/cadence/pci-j721e.c b/drivers/pci/controller/cadence/pci-j721e.c
> index a82f845cc4b5..d9b1527421c3 100644
> --- a/drivers/pci/controller/cadence/pci-j721e.c
> +++ b/drivers/pci/controller/cadence/pci-j721e.c
> @@ -43,7 +43,6 @@ enum link_status {
>  };
>  
>  #define J721E_MODE_RC			BIT(7)
> -#define LANE_COUNT_MASK			BIT(8)
>  #define LANE_COUNT(n)			((n) << 8)
>  
>  #define GENERATION_SEL_MASK		GENMASK(1, 0)
> @@ -207,11 +206,15 @@ static int j721e_pcie_set_lane_count(struct j721e_pcie *pcie,
>  {
>  	struct device *dev = pcie->cdns_pcie->dev;
>  	u32 lanes = pcie->num_lanes;
> +	u32 mask = GENMASK(8, 8);
>  	u32 val = 0;
>  	int ret;
>  
> +	if (lanes == 4)
> +		mask = GENMASK(9, 8);


Shouldn't we decide "mask" based on max_lanes added in 2/3 (ie how many
lanes HW can support and thus width of this bit field) instead of
num_lanes? Hypothetically, what if bootloader / other entity has set MSb
but Linux is restricted to 2 lanes in DT?

> +
>  	val = LANE_COUNT(lanes - 1);
> -	ret = regmap_update_bits(syscon, offset, LANE_COUNT_MASK, val);
> +	ret = regmap_update_bits(syscon, offset, mask, val);
>  	if (ret)
>  		dev_err(dev, "failed to set link count\n");
>