linux-kernel - Re: [PATCH v3 REPOST] PCIe: limit Max Read Request Size on i.MX to 512 bytes

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Date:   Tue, 16 Nov 2021 10:57:05 +0800
From:   Art Nikpal <email2tema@...il.com>
To:     Krzysztof Hałasa <khalasa@...p.pl>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        PCI <linux-pci@...r.kernel.org>,
        Neil Armstrong <narmstrong@...libre.com>,
        Huacai Chen <chenhuacai@...il.com>,
        Rob Herring <robh@...nel.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Richard Zhu <hongxing.zhu@....com>,
        Lucas Stach <l.stach@...gutronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 REPOST] PCIe: limit Max Read Request Size on i.MX to
 512 bytes

Still not merged any solution for solve this problem
same as our solution https://lkml.org/lkml/2021/7/28/1237

May be we can accept any one  ?

On Wed, Oct 6, 2021 at 2:17 PM Krzysztof Hałasa <khalasa@...p.pl> wrote:
>
> DWC PCIe controller imposes limits on the Read Request Size that it can
> handle. For i.MX6 family it's fixed at 512 bytes by default.
>
> If a memory read larger than the limit is requested, the CPU responds
> with Completer Abort (CA) (on i.MX6 Unsupported Request (UR) is returned
> instead due to a design error).
>
> The i.MX6 documentation states that the limit can be changed by writing
> to the PCIE_PL_MRCCR0 register, however there is a fixed (and
> undocumented) maximum (CX_REMOTE_RD_REQ_SIZE constant). Tests indicate
> that values larger than 512 bytes don't work, though.
>
> This patch makes the RTL8111 work on i.MX6.
>
> Signed-off-by: Krzysztof Hałasa <khalasa@...p.pl>
> ---
> While ATM needed only on ARM, this version is compiled in on all
> archs.
>
> diff --git a/drivers/pci/controller/dwc/pci-imx6.c b/drivers/pci/controller/dwc/pci-imx6.c
> index 80fc98acf097..225380e75fff 100644
> --- a/drivers/pci/controller/dwc/pci-imx6.c
> +++ b/drivers/pci/controller/dwc/pci-imx6.c
> @@ -1148,6 +1148,7 @@ static int imx6_pcie_probe(struct platform_device *pdev)
>                 imx6_pcie->vph = NULL;
>         }
>
> +       max_pcie_mrrs = 512;
>         platform_set_drvdata(pdev, imx6_pcie);
>
>         ret = imx6_pcie_attach_pd(dev);

I think next simple patch will be fine for all our cases

> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index aacf575c15cf..abeb48a64ee3 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -112,6 +112,8 @@ enum pcie_bus_config_types pcie_bus_config = PCIE_BUS_PEER2PEER;
>  enum pcie_bus_config_types pcie_bus_config = PCIE_BUS_DEFAULT;
>  #endif
>
> +u16 max_pcie_mrrs = 4096; // no limit

max_pcie_mrrs
> +
>  /*
>   * The default CLS is used if arch didn't set CLS explicitly and not
>   * all pci devices agree on the same value.  Arch can override either
> @@ -5816,6 +5818,9 @@ int pcie_set_readrq(struct pci_dev *dev, int rq)
>                         rq = mps;
>         }
>
> +       if (rq > max_pcie_mrrs)
> +               rq = max_pcie_mrrs;
> +
>         v = (ffs(rq) - 8) << 12;
>
>         ret = pcie_capability_clear_and_set_word(dev, PCI_EXP_DEVCTL,
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 06ff1186c1ef..2b95a8204819 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -996,6 +996,7 @@ enum pcie_bus_config_types {
>  };
>
>  extern enum pcie_bus_config_types pcie_bus_config;
> +extern u16 max_pcie_mrrs;
>
>  extern struct bus_type pci_bus_type;
>
>
> --
> Krzysztof "Chris" Hałasa
>
> Sieć Badawcza Łukasiewicz
> Przemysłowy Instytut Automatyki i Pomiarów PIAP
> Al. Jerozolimskie 202, 02-486 Warszawa