Re: [PATCH V5 04/16] PCI: dwc: Perform dbi regs write lock towards the end

[Vidya Sagar]

On 5/3/2019 4:43 PM, Thierry Reding wrote:
> On Wed, Apr 24, 2019 at 10:49:52AM +0530, Vidya Sagar wrote:
> > Remove multiple write enable and disable sequences of dbi registers as
> > Tegra194 implements writes to BAR-0 register (offset: 0x10) controlled by
> > DBI write-lock enable bit thereby not allowing any further writes to BAR-0
> > register in config space to take place. Hence disabling write permission
> > only towards the end.
> >
> > Signed-off-by: Vidya Sagar <vidyas@xxxxxxxxxx>
> > ---
> > Changes since [v4]:
> > * None
> >
> > Changes since [v3]:
> > * None
> >
> > Changes since [v2]:
> > * None
> >
> > Changes since [v1]:
> > * None
> >
> >   drivers/pci/controller/dwc/pcie-designware-host.c | 3 ---
> >   1 file changed, 3 deletions(-)
> >
> > diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> > index 36fd3f5b48f6..e5e3571dd2fe 100644
> > --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> > +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> > @@ -654,7 +654,6 @@ void dw_pcie_setup_rc(struct pcie_port *pp)
> >   	val &= 0xffff00ff;
> >   	val |= 0x00000100;
> >   	dw_pcie_writel_dbi(pci, PCI_INTERRUPT_LINE, val);
> > -	dw_pcie_dbi_ro_wr_dis(pci);
> >   
> >   	/* Setup bus numbers */
> >   	val = dw_pcie_readl_dbi(pci, PCI_PRIMARY_BUS);
> > @@ -686,8 +685,6 @@ void dw_pcie_setup_rc(struct pcie_port *pp)
> >   
> >   	dw_pcie_wr_own_conf(pp, PCI_BASE_ADDRESS_0, 4, 0);
> >   
> > -	/* Enable write permission for the DBI read-only register */
> > -	dw_pcie_dbi_ro_wr_en(pci);
> >   	/* Program correct class for RC */
> >   	dw_pcie_wr_own_conf(pp, PCI_CLASS_DEVICE, 2, PCI_CLASS_BRIDGE_PCI);
> >   	/* Better disable write permission right after the update */
>
> Perhaps make this explicit by moving the write enable call to the
> beginning of the function and the write disable call to the end?
>
> Currently it's pretty difficult to see where it's being disabled. Also,
> that would make it more resilient against instantiations that require a
> different register to be programmed with writes enabled.
Agree. I'll move enabling write to beginning of this function and disabling
to the end in the next patch series.

> Thierry