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

[Matt Ranostay <mranostay@ti.com>]

On Tue, Oct 25, 2022 at 05:23:20PM +0530, Vignesh Raghavendra wrote:
> 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?

Ah yes that is a very good point, and the mask should be based on max_lanes.

Will fix up in v4...

- Matt

> 
> > +
> >  	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");
> >