Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <m37dgp20cr.fsf@t19.piap.pl>
In-Reply-To: <m37dgp20cr.fsf@t19.piap.pl>
From:   Rob Herring <robh@kernel.org>
Date:   Fri, 13 Aug 2021 08:45:43 -0500
Message-ID: <CAL_JsqL1bPwbPB-3y6s0d6XoNkjrSzpbx=p7BcTq8UyTbh8pvw@mail.gmail.com>
Subject: Re: [PATCH] PCIe: limit Max Read Request Size on i.MX to 512 bytes
To:     =?UTF-8?Q?Krzysztof_Ha=C5=82asa?= <khalasa@piap.pl>
Cc:     Bjorn Helgaas <bhelgaas@google.com>,
        PCI <linux-pci@vger.kernel.org>,
        Artem Lapkin <email2tema@gmail.com>,
        Neil Armstrong <narmstrong@baylibre.com>,
        Huacai Chen <chenhuacai@gmail.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        =?UTF-8?Q?Krzysztof_Wilczy=C5=84ski?= <kw@linux.com>,
        Richard Zhu <hongxing.zhu@nxp.com>,
        Lucas Stach <l.stach@pengutronix.de>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Fri, Aug 13, 2021 at 3:52 AM Krzysztof Ha=C5=82asa <khalasa@piap.pl> wro=
te:
>
> 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 Ha=C5=82asa <khalasa@piap.pl>
>
> diff --git a/drivers/pci/Kconfig b/drivers/pci/Kconfig
> index 0c473d75e625..a11ec93a8cd0 100644
> --- a/drivers/pci/Kconfig
> +++ b/drivers/pci/Kconfig
> @@ -34,6 +34,9 @@ config PCI_DOMAINS_GENERIC
>  config PCI_SYSCALL
>         bool
>
> +config NEED_PCIE_MAX_MRRS

We don't need a config option for this. It's not much code and it will
effectively always be enabled with multi-platform kernels.

Rob