linux-kernel - Re: [PATCH] PCI: keystone: Add workaround for Errata #i2037 (AM65x SR 1.0)

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Date: Thu, 27 Jun 2024 17:54:44 +0530
From: Siddharth Vadapalli <s-vadapalli@...com>
To: Jan Kiszka <jan.kiszka@...mens.com>,
        Krzysztof Wilczyński
	<kw@...ux.com>
CC: Lorenzo Pieralisi <lpieralisi@...nel.org>, Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Kishon Vijay Abraham I
	<kishon@...nel.org>,
        Siddharth Vadapalli <s-vadapalli@...com>,
        Vignesh
 Raghavendra <vigneshr@...com>, Nishanth Menon <nm@...com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        Linux Kernel Mailing
 List <linux-kernel@...r.kernel.org>,
        linux-arm-kernel
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] PCI: keystone: Add workaround for Errata #i2037 (AM65x
 SR 1.0)

On Wed, Jun 26, 2024 at 12:10:41AM +0200, Jan Kiszka wrote:
> From: Kishon Vijay Abraham I <kishon@...com>
> 
> Errata #i2037 in AM65x/DRA80xM Processors Silicon Revision 1.0
> (SPRZ452D_July 2018_Revised December 2019 [1]) mentions when an
> inbound PCIe TLP spans more than two internal AXI 128-byte bursts,
> the bus may corrupt the packet payload and the corrupt data may
> cause associated applications or the processor to hang.
> 
> The workaround for Errata #i2037 is to limit the maximum read
> request size and maximum payload size to 128 Bytes. Add workaround
> for Errata #i2037 here. The errata and workaround is applicable
> only to AM65x SR 1.0 and later versions of the silicon will have
> this fixed.
> 
> [1] -> http://www.ti.com/lit/er/sprz452d/sprz452d.pdf
> 
> Signed-off-by: Kishon Vijay Abraham I <kishon@...com>
> Signed-off-by: Achal Verma <a-verma1@...com>
> Link: https://lore.kernel.org/linux-pci/20210325090026.8843-7-kishon@ti.com/

Please drop the above. It needs to be mentioned as the v1 below the
tear-line.

> Signed-off-by: Vignesh Raghavendra <vigneshr@...com>
> Signed-off-by: Jan Kiszka <jan.kiszka@...mens.com>
> ---
> 
> Needed for the IOT2050 PG1 variants. Pending downstream way too long.
> 
>  drivers/pci/controller/dwc/pci-keystone.c | 42 +++++++++++++++++++++++
>  1 file changed, 42 insertions(+)
> 
> diff --git a/drivers/pci/controller/dwc/pci-keystone.c b/drivers/pci/controller/dwc/pci-keystone.c
> index d3a7d14ee685..a04f1087ce91 100644
> --- a/drivers/pci/controller/dwc/pci-keystone.c
> +++ b/drivers/pci/controller/dwc/pci-keystone.c
> @@ -34,6 +34,11 @@
>  #define PCIE_DEVICEID_SHIFT	16

[...]

>  
> +	static const struct pci_device_id am6_pci_devids[] = {
> +		{ PCI_DEVICE(PCI_VENDOR_ID_TI, PCI_DEVICE_ID_TI_AM654X),
> +		 .class = PCI_CLASS_BRIDGE_PCI << 8, .class_mask = ~0, },
> +		{ 0, },
> +	};
>  
>  	if (pci_is_root_bus(bus))
>  		bridge = dev;
> @@ -562,6 +578,32 @@ static void ks_pcie_quirk(struct pci_dev *dev)
>  			pcie_set_readrq(dev, 256);
>  		}
>  	}
> +
> +	/*
> +	 * Memory transactions fail with PCI controller in AM654 PG1.0
> +	 * when MRRS is set to more than 128 Bytes. Force the MRRS to
> +	 * 128 Bytes in all downstream devices.
> +	 */

Comments on the v1 patch at:
https://lore.kernel.org/linux-pci/YF2K6+R1P3SNUoo5@rocinante/
haven't been addressed in this patch. Kindly update the patch based on
Krzysztof's feedback on the v1 patch.

> +	if (pci_match_id(am6_pci_devids, bridge)) {
> +		bridge_dev = pci_get_host_bridge_device(dev);
> +		if (!bridge_dev && !bridge_dev->parent)
> +			return;
> +
> +		ks_pcie = dev_get_drvdata(bridge_dev->parent);
> +		if (!ks_pcie)
> +			return;
> +
> +		val = ks_pcie_app_readl(ks_pcie, PID);
> +		val &= RTL;
> +		val >>= RTL_SHIFT;
> +		if (val != AM6_PCI_PG1_RTL_VER)
> +			return;
> +
> +		if (pcie_get_readrq(dev) > 128) {
> +			dev_info(&dev->dev, "limiting MRRS to 128\n");
> +			pcie_set_readrq(dev, 128);
> +		}
> +	}
>  }
>  DECLARE_PCI_FIXUP_ENABLE(PCI_ANY_ID, PCI_ANY_ID, ks_pcie_quirk);

Regards,
Siddharth.