linux-kernel - Re: [PATCH 1/1] PCI: iproc: Invalidate PAXB address mapping before programming it

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Message-ID: <20190906100114.GE9720@e119886-lin.cambridge.arm.com>
Date:   Fri, 6 Sep 2019 11:01:14 +0100
From:   Andrew Murray <andrew.murray@....com>
To:     Abhishek Shah <abhishek.shah@...adcom.com>
Cc:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        linux-pci@...r.kernel.org,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>,
        BCM Kernel Feedback <bcm-kernel-feedback-list@...adcom.com>
Subject: Re: [PATCH 1/1] PCI: iproc: Invalidate PAXB address mapping before
 programming it

On Fri, Sep 06, 2019 at 02:55:19PM +0530, Abhishek Shah wrote:
> Hi Andrew,
> 
> Thanks for the review. Please see my response inline:
> 
> On Fri, Sep 6, 2019 at 2:08 PM Andrew Murray <andrew.murray@....com> wrote:
> >
> > On Fri, Sep 06, 2019 at 09:28:13AM +0530, Abhishek Shah wrote:
> > > Invalidate PAXB inbound/outbound address mapping each time before
> > > programming it. This is helpful for the cases where we need to
> > > reprogram inbound/outbound address mapping without resetting PAXB.
> > > kexec kernel is one such example.
> >
> > Why is this approach better than resetting the PAXB (I assume that's
> > the PCI controller IP)? Wouldn't resetting the PAXB address this issue,
> > and ensure that no other configuration is left behind?
> >
> We normally reset PAXB in the firmware(ATF). But for cases like kexec
> kernel boot,
> we do not execute any firmware code and directly boot into kernel.
> 
> We could have done PAXB reset in the driver itself as you have suggested here.
> But note that this detail could vary for each SoC, because these
> registers are not part
> of PAXB register space itself, rather exists in a register space responsible for
> controlling power to various wrappers in PCIe IP. Normally, this kind
> of SoC specific
> details are handled in firmware itself, we don't bring them to driver level.

OK understood.

> 
> > Or is this related to earlier boot stages loading firmware for the emulated
> > downstream endpoints (ep_is_internal)?
> >
> > Finally, in the case where ep_is_internal do you need to disable anything
> > prior to invalidating the mappings?
> >
> No, ep_is_internal  is indicator for PAXC IP. It does not have
> mappings as in PAXB.

I think I meant !ep_is_internal. I.e. is there possibility of inbound traffic
prior to invalidating the mappings. I'd assume not, but that's an assumption.

Either way:

Reviewed-by: Andrew Murray <andrew.murray@....com>

> 
> 
> Regards,
> Abhishek
> > >
> > > Signed-off-by: Abhishek Shah <abhishek.shah@...adcom.com>
> > > Reviewed-by: Ray Jui <ray.jui@...adcom.com>
> > > Reviewed-by: Vikram Mysore Prakash <vikram.prakash@...adcom.com>
> > > ---
> > >  drivers/pci/controller/pcie-iproc.c | 28 ++++++++++++++++++++++++++++
> > >  1 file changed, 28 insertions(+)
> > >
> > > diff --git a/drivers/pci/controller/pcie-iproc.c b/drivers/pci/controller/pcie-iproc.c
> > > index e3ca46497470..99a9521ba7ab 100644
> > > --- a/drivers/pci/controller/pcie-iproc.c
> > > +++ b/drivers/pci/controller/pcie-iproc.c
> > > @@ -1245,6 +1245,32 @@ static int iproc_pcie_map_dma_ranges(struct iproc_pcie *pcie)
> > >       return ret;
> > >  }
> > >
> > > +static void iproc_pcie_invalidate_mapping(struct iproc_pcie *pcie)
> > > +{
> > > +     struct iproc_pcie_ib *ib = &pcie->ib;
> > > +     struct iproc_pcie_ob *ob = &pcie->ob;
> > > +     int idx;
> > > +
> > > +     if (pcie->ep_is_internal)
> > > +             return;
> > > +
> > > +     if (pcie->need_ob_cfg) {
> > > +             /* iterate through all OARR mapping regions */
> > > +             for (idx = ob->nr_windows - 1; idx >= 0; idx--) {
> > > +                     iproc_pcie_write_reg(pcie,
> > > +                                          MAP_REG(IPROC_PCIE_OARR0, idx), 0);
> > > +             }
> > > +     }
> > > +
> > > +     if (pcie->need_ib_cfg) {
> > > +             /* iterate through all IARR mapping regions */
> > > +             for (idx = 0; idx < ib->nr_regions; idx++) {
> > > +                     iproc_pcie_write_reg(pcie,
> > > +                                          MAP_REG(IPROC_PCIE_IARR0, idx), 0);
> > > +             }
> > > +     }
> > > +}
> > > +
> > >  static int iproce_pcie_get_msi(struct iproc_pcie *pcie,
> > >                              struct device_node *msi_node,
> > >                              u64 *msi_addr)
> > > @@ -1517,6 +1543,8 @@ int iproc_pcie_setup(struct iproc_pcie *pcie, struct list_head *res)
> > >       iproc_pcie_perst_ctrl(pcie, true);
> > >       iproc_pcie_perst_ctrl(pcie, false);
> > >
> > > +     iproc_pcie_invalidate_mapping(pcie);
> > > +
> > >       if (pcie->need_ob_cfg) {
> > >               ret = iproc_pcie_map_ranges(pcie, res);
> > >               if (ret) {
> >
> > The code changes look good to me.
> >
> > Thanks,
> >
> > Andrew Murray
> >
> > > --
> > > 2.17.1
> > >