RE: [PATCH v3 2/2] PCI: xilinx-nwl: Increase ECAM size to accommodate 256 buses

[Havalige, Thippeswamy]

Hi Rob,

> -----Original Message-----
> From: Rob Herring <robh@xxxxxxxxxx>
> Sent: Friday, August 11, 2023 2:47 AM
> To: Havalige, Thippeswamy <thippeswamy.havalige@xxxxxxx>
> Cc: linux-kernel@xxxxxxxxxxxxxxx; bhelgaas@xxxxxxxxxx;
> krzysztof.kozlowski@xxxxxxxxxx; linux-pci@xxxxxxxxxxxxxxx;
> devicetree@xxxxxxxxxxxxxxx; conor+dt@xxxxxxxxxx; lpieralisi@xxxxxxxxxx;
> Gogada, Bharat Kumar <bharat.kumar.gogada@xxxxxxx>; Simek, Michal
> <michal.simek@xxxxxxx>; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [PATCH v3 2/2] PCI: xilinx-nwl: Increase ECAM size to
> accommodate 256 buses
> 
> On Thu, Aug 10, 2023 at 05:50:02PM +0530, Thippeswamy Havalige wrote:
> > Our controller is expecting ECAM size to be programmed by software. By
> > programming "NWL_ECAM_VALUE_DEFAULT  12" controller can access up to
> > 16MB ECAM region which is used to detect 16 buses, so by updating
> > "NWL_ECAM_VALUE_DEFAULT" to 16 so that controller can access up to
> > 256MB ECAM region to detect 256 buses.
> 
> What happens when your DT has the smaller size and the kernel configures
> the larger size? Seems like you could have an ABI issue.
- Here we are enabling hardware to support maximum buses. In this case kernel can enumerate up to device tree exposed ECAM size. 
We will not face any issue.
> >
> > Signed-off-by: Thippeswamy Havalige <thippeswamy.havalige@xxxxxxx>
> > Signed-off-by: Bharat Kumar Gogada <bharat.kumar.gogada@xxxxxxx>
> > ---
> > changes in v3:
> > - Remove unnecessary period at end of subject line.
> > changes in v2:
> > - Update this changes in a seperate patch.
> > ---
> >  drivers/pci/controller/pcie-xilinx-nwl.c | 6 ++----
> >  1 file changed, 2 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/pci/controller/pcie-xilinx-nwl.c
> > b/drivers/pci/controller/pcie-xilinx-nwl.c
> > index d8a3a08be1d5..b51501921d3b 100644
> > --- a/drivers/pci/controller/pcie-xilinx-nwl.c
> > +++ b/drivers/pci/controller/pcie-xilinx-nwl.c
> > @@ -126,7 +126,7 @@
> >  #define E_ECAM_CR_ENABLE		BIT(0)
> >  #define E_ECAM_SIZE_LOC			GENMASK(20, 16)
> >  #define E_ECAM_SIZE_SHIFT		16
> > -#define NWL_ECAM_VALUE_DEFAULT		12
> > +#define NWL_ECAM_VALUE_DEFAULT		16
 - Agreed, ll fix it in next patch.
> Not really a meaningful name. It doesn't explain what '16' means.
> 
> >  #define CFG_DMA_REG_BAR			GENMASK(2, 0)
> >  #define CFG_PCIE_CACHE			GENMASK(7, 0)
> > @@ -165,7 +165,6 @@ struct nwl_pcie {
> >  	u32 ecam_size;
> >  	int irq_intx;
> >  	int irq_misc;
> > -	u32 ecam_value;
> >  	struct nwl_msi msi;
> >  	struct irq_domain *legacy_irq_domain;
> >  	struct clk *clk;
> > @@ -674,7 +673,7 @@ static int nwl_pcie_bridge_init(struct nwl_pcie *pcie)
> >  			  E_ECAM_CR_ENABLE, E_ECAM_CONTROL);
> >
> >  	nwl_bridge_writel(pcie, nwl_bridge_readl(pcie, E_ECAM_CONTROL) |
> > -			  (pcie->ecam_value << E_ECAM_SIZE_SHIFT),
> > +			  (NWL_ECAM_VALUE_DEFAULT <<
> E_ECAM_SIZE_SHIFT),
> >  			  E_ECAM_CONTROL);
> >
> >  	nwl_bridge_writel(pcie, lower_32_bits(pcie->phys_ecam_base),
> > @@ -782,7 +781,6 @@ static int nwl_pcie_probe(struct platform_device
> *pdev)
> >  	pcie = pci_host_bridge_priv(bridge);
> >
> >  	pcie->dev = dev;
> > -	pcie->ecam_value = NWL_ECAM_VALUE_DEFAULT;
> >
> >  	err = nwl_pcie_parse_dt(pcie, pdev);
> >  	if (err) {
> > --
> > 2.17.1
> >