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

[Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>]

On Thu, Jun 27, 2019 at 09:03:08PM +0530, Vidya Sagar wrote:
> 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.

Ok, so DBI space registers that require write permissions are per-IP.
This is clearer so the commit log must be rewritten, it is not clear at
all in this respect at least not as-is, if you read it you will
notice ;-)

Lorenzo

> 
> -Vidya Sagar
> 
> > 
> > > Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
> > > Reviewed-by: Thierry Reding <treding@nvidia.com>
> > > Acked-by: Jingoo Han <jingoohan1@gmail.com>
> > > ---
> > > 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
> > > 
>