Re: [PATCH V11 03/12] PCI: dwc: Perform dbi regs write lock towards the end

[Vidya Sagar <vidyas@xxxxxxxxxx>]

On 6/27/2019 8:28 PM, Lorenzo Pieralisi wrote:
> On Mon, Jun 24, 2019 at 02:44:56PM +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 enabling write permission at
> > the start of function and disabling the same only towards the end.
>
> I do not understand what this patch does, I would like to rephrase
> the commit log in a way that is easier to parse.
>
> In particular I do not get what you mean in relation to BAR-0, I am
> confused, please clarify.
>
> Lorenzo
Well, some of the Synopsys DesignWare core's DBI registers are protected with a lock
without which, they are read-only by default. Existing code in dw_pcie_setup_rc() API
tries to unlock and lock multiple times whenever it wants to update those write-protected
registers. This patch attempts to unlock all such write-protected registers for writing
once in the beginning of the function and lock them back towards the end.
As far as BAR-0 register (which is at offset 0x10 in DBI space... nothing but the
config space) in Tegra194 is concerned, it is one of those registers to which
writes are protected. I could have added unlock/lock pair around accessing this register,
but that would bloat this API with one more pair of unlock/lock, instead I chose to remove
unlock/lock pairs for all protected registers and have unlock in the beginning and lock
towards the end.

-Vidya Sagar

> > Signed-off-by: Vidya Sagar <vidyas@xxxxxxxxxx>
> > Reviewed-by: Thierry Reding <treding@xxxxxxxxxx>
> > Acked-by: Jingoo Han <jingoohan1@xxxxxxxxx>
> > ---
> > Changes since [v10]:
> > * None
> >
> > Changes since [v9]:
> > * None
> >
> > Changes since [v8]:
> > * None
> >
> > Changes since [v7]:
> > * None
> >
> > Changes since [v6]:
> > * None
> >
> > Changes since [v5]:
> > * Moved write enable to the beginning of the API and write disable to the end
> >
> > Changes since [v4]:
> > * None
> >
> > Changes since [v3]:
> > * None
> >
> > Changes since [v2]:
> > * None
> >
> > Changes since [v1]:
> > * None
> >
> >   drivers/pci/controller/dwc/pcie-designware-host.c | 14 ++++++++------
> >   1 file changed, 8 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> > index f93252d0da5b..d3156446ff27 100644
> > --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> > +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> > @@ -628,6 +628,12 @@ void dw_pcie_setup_rc(struct pcie_port *pp)
> >   	u32 val, ctrl, num_ctrls;
> >   	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
> >   
> > +	/*
> > +	 * Enable DBI read-only registers for writing/updating configuration.
> > +	 * Write permission gets disabled towards the end of this function.
> > +	 */
> > +	dw_pcie_dbi_ro_wr_en(pci);
> > +
> >   	dw_pcie_setup(pci);
> >   
> >   	if (!pp->ops->msi_host_init) {
> > @@ -650,12 +656,10 @@ void dw_pcie_setup_rc(struct pcie_port *pp)
> >   	dw_pcie_writel_dbi(pci, PCI_BASE_ADDRESS_1, 0x00000000);
> >   
> >   	/* Setup interrupt pins */
> > -	dw_pcie_dbi_ro_wr_en(pci);
> >   	val = dw_pcie_readl_dbi(pci, PCI_INTERRUPT_LINE);
> >   	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);
> > @@ -687,15 +691,13 @@ 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 */
> > -	dw_pcie_dbi_ro_wr_dis(pci);
> >   
> >   	dw_pcie_rd_own_conf(pp, PCIE_LINK_WIDTH_SPEED_CONTROL, 4, &val);
> >   	val |= PORT_LOGIC_SPEED_CHANGE;
> >   	dw_pcie_wr_own_conf(pp, PCIE_LINK_WIDTH_SPEED_CONTROL, 4, val);
> > +
> > +	dw_pcie_dbi_ro_wr_dis(pci);
> >   }
> >   EXPORT_SYMBOL_GPL(dw_pcie_setup_rc);
> > --
> > 2.17.1