linux-kernel - Re: [PATCH v4 06/10] PCI: brcmstb: Enable external MSI-X if available

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Message-ID: <CA+-6iNytvANeUb3ugW0q3B18MTNwnJps_yggonKRjXh_sTWHmA@mail.gmail.com>
Date: Wed, 18 Dec 2024 11:20:26 -0500
From: Jim Quinlan <james.quinlan@...adcom.com>
To: Stanimir Varbanov <svarbanov@...e.de>
Cc: linux-kernel@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-rpi-kernel@...ts.infradead.org, 
	linux-pci@...r.kernel.org, 
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>, 
	Thomas Gleixner <tglx@...utronix.de>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Florian Fainelli <florian.fainelli@...adcom.com>, Jim Quinlan <jim2101024@...il.com>, 
	Nicolas Saenz Julienne <nsaenz@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>, 
	Lorenzo Pieralisi <lpieralisi@...nel.org>, kw@...ux.com, 
	Philipp Zabel <p.zabel@...gutronix.de>, Andrea della Porta <andrea.porta@...e.com>, 
	Phil Elwell <phil@...pberrypi.com>, Jonathan Bell <jonathan@...pberrypi.com>
Subject: Re: [PATCH v4 06/10] PCI: brcmstb: Enable external MSI-X if available

On Wed, Dec 18, 2024 at 9:54 AM Stanimir Varbanov <svarbanov@...e.de> wrote:
>
> Hi Jim,
>
> Thanks for comments!
>
> On 12/11/24 10:01 PM, James Quinlan wrote:
> > On 10/25/24 08:45, Stanimir Varbanov wrote:
> >> On RPi5 there is an external MIP MSI-X interrupt controller
> >> which can handle up to 64 interrupts.
> >>
> >> Signed-off-by: Stanimir Varbanov <svarbanov@...e.de>
> >> ---
> >> v3 -> v4:
> >>   - no changes.
> >>
> >>   drivers/pci/controller/pcie-brcmstb.c | 63 +++++++++++++++++++++++++--
> >>   1 file changed, 59 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/drivers/pci/controller/pcie-brcmstb.c b/drivers/pci/
> >> controller/pcie-brcmstb.c
> >> index c01462b07eea..af01a7915c94 100644
> >> --- a/drivers/pci/controller/pcie-brcmstb.c
> >> +++ b/drivers/pci/controller/pcie-brcmstb.c
> >> @@ -1318,6 +1318,52 @@ static int brcm_pcie_start_link(struct
> >> brcm_pcie *pcie)
> >>       return 0;
> >>   }
> >>   +static int brcm_pcie_enable_external_msix(struct brcm_pcie *pcie,
> >> +                      struct device_node *msi_np)
> >> +{
> >> +    struct inbound_win inbound_wins[PCIE_BRCM_MAX_INBOUND_WINS];
> >> +    u64 msi_pci_addr, msi_phys_addr;
> >> +    struct resource r;
> >> +    int mip_bar, ret;
> >> +    u32 val, reg;
> >> +
> >> +    ret = of_property_read_reg(msi_np, 1, &msi_pci_addr, NULL);
> >> +    if (ret)
> >> +        return ret;
> >> +
> >> +    ret = of_address_to_resource(msi_np, 0, &r);
> >> +    if (ret)
> >> +        return ret;
> >> +
> >> +    msi_phys_addr = r.start;
> >> +
> >> +    /* Find free inbound window for MIP access */
> >> +    mip_bar = brcm_pcie_get_inbound_wins(pcie, inbound_wins);
> >> +    if (mip_bar < 0)
> >> +        return mip_bar;
> >> +
> >> +    mip_bar += 1;
> >> +    reg = brcm_bar_reg_offset(mip_bar);
> >> +
> >> +    val = lower_32_bits(msi_pci_addr);
> >> +    val |= brcm_pcie_encode_ibar_size(SZ_4K);
> >> +    writel(val, pcie->base + reg);
> >> +
> >> +    val = upper_32_bits(msi_pci_addr);
> >> +    writel(val, pcie->base + reg + 4);
> >> +
> >> +    reg = brcm_ubus_reg_offset(mip_bar);
> >> +
> >> +    val = lower_32_bits(msi_phys_addr);
> >> +    val |= PCIE_MISC_UBUS_BAR1_CONFIG_REMAP_ACCESS_EN_MASK;
> >> +    writel(val, pcie->base + reg);
> >> +
> >> +    val = upper_32_bits(msi_phys_addr);
> >> +    writel(val, pcie->base + reg + 4);
> >
> > Hi Stan,
> >
> > It looks like all this is doing is setting up an identity-mapped inbound
> > window, is that correct?  If so, couldn't you get the same effect by
> > adding an identity-mapped dma-range in the PCIe DT node?
>
> Yes, that approach could work, I verified it.
>
> Do you want me to drop this patch from the series and make the relevant
> changes in PCIe dma-ranges properties?
>
Hi Stan,

Yes please, that was what I was hoping for -- the less code the
better, assuming everything still works :-)

Thanks & regards,
Jim Quinlan
Broadcom STB/CM

> ~Stan
>
>
>

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