linux-kernel - Re: [PATCH 6/6] PCI: keystone: Add workaround for Errata #i2037 (AM65x SR 1.0)

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Message-ID: <YF2K6+R1P3SNUoo5@rocinante>
Date:   Fri, 26 Mar 2021 08:19:07 +0100
From:   Krzysztof Wilczyński <kw@...ux.com>
To:     Kishon Vijay Abraham I <kishon@...com>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Rob Herring <robh+dt@...nel.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Marc Zyngier <maz@...nel.org>, linux-pci@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Lokesh Vutla <lokeshvutla@...com>
Subject: Re: [PATCH 6/6] PCI: keystone: Add workaround for Errata #i2037
 (AM65x SR 1.0)

Hi Kishon,

A few small nitpicks.

> 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.

I think it would be either "128 B" or "128 bytes", there is no need to
capitalise bytes.

[...]
> +	/*
> +	 * 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.
> +	 */

Same here, it would be "128 bytes" in the comment above.

[...]
> +		if (pcie_get_readrq(dev) > 128) {
> +			dev_info(&dev->dev, "limiting MRRS to 128\n");
> +			pcie_set_readrq(dev, 128);
> +		}
[...]

Might be nice to add unit here, so "128 bytes".

Krzysztof