linux-kernel - RE: [PATCH] PCI: dwc: Add upper limit address for outbound iATU

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Date:   Thu, 24 Dec 2020 11:06:50 +0530
From:   "Shradha Todi" <shradha.t@...sung.com>
To:     "'Rob Herring'" <robh@...nel.org>
Cc:     <linux-kernel@...r.kernel.org>,
        "'PCI'" <linux-pci@...r.kernel.org>,
        "'Jingoo Han'" <jingoohan1@...il.com>,
        "'Gustavo Pimentel'" <gustavo.pimentel@...opsys.com>,
        "'Lorenzo Pieralisi'" <lorenzo.pieralisi@....com>,
        "'Bjorn Helgaas'" <bhelgaas@...gle.com>,
        "'Pankaj Dubey'" <pankaj.dubey@...sung.com>
Subject: RE: [PATCH] PCI: dwc: Add upper limit address for outbound iATU

> From: Rob Herring <robh@...nel.org>
> Subject: Re: [PATCH] PCI: dwc: Add upper limit address for outbound iATU
> 
> On Sun, Dec 20, 2020 at 6:56 PM Shradha Todi <shradha.t@...sung.com>
> wrote:
> >
> > The size parameter is unsigned long type which can accept size > 4GB.
> > In that case, the upper limit address must be programmed. Add support
> > to program the upper limit address and set INCREASE_REGION_SIZE in
> > case size > 4GB.
> 
> Not all DWC h/w versions have the upper register and bit. Is it safe to write to
> the non-existent register?

Thanks for the review.
Surely it exists post 4.80a version of controller but I am not sure in 
which version of the controller this was introduced. I can figure this
out from the SNPS team and update the patch accordingly.

> 
> >
> > Signed-off-by: Shradha Todi <shradha.t@...sung.com>
> > ---
> >  drivers/pci/controller/dwc/pcie-designware.c | 8 ++++++--
> > drivers/pci/controller/dwc/pcie-designware.h | 1 +
> >  2 files changed, 7 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/pci/controller/dwc/pcie-designware.c
> > b/drivers/pci/controller/dwc/pcie-designware.c
> > index 28c56a1..7eba3b2 100644
> > --- a/drivers/pci/controller/dwc/pcie-designware.c
> > +++ b/drivers/pci/controller/dwc/pcie-designware.c
> > @@ -290,12 +290,16 @@ static void __dw_pcie_prog_outbound_atu(struct
> dw_pcie *pci, u8 func_no,
> >                            upper_32_bits(cpu_addr));
> >         dw_pcie_writel_dbi(pci, PCIE_ATU_LIMIT,
> >                            lower_32_bits(cpu_addr + size - 1));
> > +       dw_pcie_writel_dbi(pci, PCIE_ATU_UPPER_LIMIT,
> > +                          upper_32_bits(cpu_addr + size - 1));
> 
> If not safe, perhaps only write if non-zero.
> 
Writing zero has no side-affect and we have tested this.

> >         dw_pcie_writel_dbi(pci, PCIE_ATU_LOWER_TARGET,
> >                            lower_32_bits(pci_addr));
> >         dw_pcie_writel_dbi(pci, PCIE_ATU_UPPER_TARGET,
> >                            upper_32_bits(pci_addr));
> > -       dw_pcie_writel_dbi(pci, PCIE_ATU_CR1, type |
> > -                          PCIE_ATU_FUNC_NUM(func_no));
> > +       val = type | PCIE_ATU_FUNC_NUM(func_no);
> > +       val = upper_32_bits(size - 1) ?
> > +               val | PCIE_ATU_INCREASE_REGION_SIZE : val;
> > +       dw_pcie_writel_dbi(pci, PCIE_ATU_CR1, val);
> >         dw_pcie_writel_dbi(pci, PCIE_ATU_CR2, PCIE_ATU_ENABLE);
> >
> >         /*
> > diff --git a/drivers/pci/controller/dwc/pcie-designware.h
> > b/drivers/pci/controller/dwc/pcie-designware.h
> > index b09329b..28b72fb 100644
> > --- a/drivers/pci/controller/dwc/pcie-designware.h
> > +++ b/drivers/pci/controller/dwc/pcie-designware.h
> > @@ -106,6 +106,7 @@
> >  #define PCIE_ATU_DEV(x)                        FIELD_PREP(GENMASK(23, 19), x)
> >  #define PCIE_ATU_FUNC(x)               FIELD_PREP(GENMASK(18, 16), x)
> >  #define PCIE_ATU_UPPER_TARGET          0x91C
> > +#define PCIE_ATU_UPPER_LIMIT           0x924
> >
> >  #define PCIE_MISC_CONTROL_1_OFF                0x8BC
> >  #define PCIE_DBI_RO_WR_EN              BIT(0)
> > --
> > 2.7.4
> >