linux-kernel - Re: [PATCH v2 0/2] PCI: xgene: Restore working PCIe functionnality

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Date:   Mon, 21 Mar 2022 16:32:40 -0600
From:   dann frazier <dann.frazier@...onical.com>
To:     Rob Herring <robh@...nel.org>
Cc:     Marc Zyngier <maz@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        PCI <linux-pci@...r.kernel.org>,
        Toan Le <toan@...amperecomputing.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Stéphane Graber <stgraber@...ntu.com>,
        Android Kernel Team <kernel-team@...roid.com>
Subject: Re: [PATCH v2 0/2] PCI: xgene: Restore working PCIe functionnality

On Mon, Mar 21, 2022 at 11:08:20AM -0500, Rob Herring wrote:
> On Mon, Mar 21, 2022 at 09:50:24AM -0600, dann frazier wrote:
> > On Mon, Mar 21, 2022 at 10:17:34AM -0500, Rob Herring wrote:
> > > On Mon, Mar 21, 2022 at 5:49 AM Marc Zyngier <maz@...nel.org> wrote:
> > > >
> > > > Since 6dce5aa59e0b ("PCI: xgene: Use inbound resources for setup") was
> > > > merged in the 5.5 time frame, PCIe on the venerable XGene platform has
> > > > been unusable: 6dce5aa59e0b broke both XGene-1 (Mustang and m400) and
> > > > XGene-2 (Merlin), while the addition of c7a75d07827a ("PCI: xgene: Fix
> > > > IB window setup") fixed XGene-2, but left the rest of the zoo
> > > > unusable.
> > > >
> > > > It is understood that this systems come with "creative" DTs that don't
> > > > match the expectations of modern kernels. However, there is little to
> > > > be gained by forcing these changes on users -- the firmware is not
> > > > upgradable, and the current owner of the IP will deny that these
> > > > machines have ever existed.
> > > 
> > > The gain for fixing this properly is not having drivers do their own
> > > dma-ranges parsing. We've seen what happens when drivers do their own
> > > parsing of standard properties (e.g. interrupt-map). Currently, we
> > > don't have any drivers doing their own parsing:
> > > 
> > > $ git grep of_pci_dma_range_parser_init
> > > drivers/of/address.c:int of_pci_dma_range_parser_init(struct
> > > of_pci_range_parser *parser,
> > > drivers/of/address.c:EXPORT_SYMBOL_GPL(of_pci_dma_range_parser_init);
> > > drivers/of/address.c:#define of_dma_range_parser_init
> > > of_pci_dma_range_parser_init
> > > drivers/of/unittest.c:  if (of_pci_dma_range_parser_init(&parser, np)) {
> > > drivers/pci/of.c:       err = of_pci_dma_range_parser_init(&parser, dev_node);
> > > include/linux/of_address.h:extern int
> > > of_pci_dma_range_parser_init(struct of_pci_range_parser *parser,
> > > include/linux/of_address.h:static inline int
> > > of_pci_dma_range_parser_init(struct of_pci_range_parser *parser,
> > > 
> > > And we can probably further refactor this to be private to drivers/pci/of.c.
> > > 
> > > For XGene-2 the issue is simply that the driver depends on the order
> > > of dma-ranges entries.
> > > 
> > > For XGene-1, I'd still like to understand what the issue is. Reverting
> > > the first fix and fixing 'dma-ranges' should have fixed it. I need a
> > > dump of how the IB registers are initialized in both cases.
> > 
> > Happy to provide that for the m400 if told how :)
> 
> Something like the below patch. This should be with the 'dma-ranges' 
> DT change and only c7a75d07827a reverted.

https://paste.ubuntu.com/p/RHzBd5jT6v/

Note that networking does come up with this setup. That surprised me
because I thought I'd tested this combo before, but apparently what
I'd tested before was 6dce5aa59e0b reverted + the dtb change:
  https://lore.kernel.org/linux-pci/YgXG838iMrS1l8SC@xps13.dannf/

  -dann


> 8<-------------------------------------------------------------------
> diff --git a/drivers/pci/controller/pci-xgene.c b/drivers/pci/controller/pci-xgene.c
> index 0d5acbfc7143..6a435c31f45e 100644
> --- a/drivers/pci/controller/pci-xgene.c
> +++ b/drivers/pci/controller/pci-xgene.c
> @@ -78,6 +78,7 @@ static u32 xgene_pcie_readl(struct xgene_pcie *port, u32 reg)
>  
>  static void xgene_pcie_writel(struct xgene_pcie *port, u32 reg, u32 val)
>  {
> +	dev_info(port->dev, "0x%04x <- 0x%08x\n", reg, val);
>  	writel(val, port->csr_base + reg);
>  }
>  
> @@ -508,7 +509,9 @@ static void xgene_pcie_setup_ib_reg(struct xgene_pcie *port,
>  	case 0:
>  		xgene_pcie_set_ib_mask(port, BRIDGE_CFG_4, flags, size);
>  		bar_addr = cfg_base + PCI_BASE_ADDRESS_0;
> +		dev_info(port->dev, "BAR0L <- 0x%08x\n", bar_low);
>  		writel(bar_low, bar_addr);
> +		dev_info(port->dev, "BAR0H <- 0x%08x\n", upper_32_bits(cpu_addr));
>  		writel(upper_32_bits(cpu_addr), bar_addr + 0x4);
>  		pim_reg = PIM1_1L;
>  		break;