Re: [PATCH 0/3] PCI:?==?utf-8?q? rockchip: 5.0 GT/s speed may be dangerous

[Dragan Simic]

Hello Shawn and Geraldo,

On Monday, November 17, 2025 04:42 CET, Shawn Lin <shawn.lin at rock-chips.com> wrote:
> 在 2025/11/15 星期六 17:10, Geraldo Nascimento 写道:
> > In recent interactions with Shawn Lin from Rockchip it came to my
> > attention there's an unknown errata regarding 5.0 GT/s operational
> > speed of their PCIe core. According to Shawn there's grave danger
> > even if the odds are low. To contain any damage, let's cover the
> > remaining corner-cases where the default would lead to 5.0 GT/s
> > operation as well as add a comment to Root Complex driver core,
> > documenting this danger.
> 
> I'm not sure just adding a warn would be a good choice. Could we totally
> force to use gen1 and add a warn if trying to use Gen2.

I think that forcing 2.5 GT/s with an appropriate warning message
is a good idea.  That would be like some quirk that gets applied
automatically, to prevent data corruption, while warning people
who attempt to "overclock" the PCIe interface.

> Meanwhile amend the commit message to add a reference
> of RK3399 official datesheet[1] which says PCIe on RK3399 should only
> support 2.5GT/s?
> 
> [1]https://opensource.rock-chips.com/images/d/d7/Rockchip_RK3399_Datasheet_V2.1-20200323.pdf

Also, rewording the patch summary as follows below may be good,
because that would provide more details:

  PCI: rockchip: Warn about Gen2 5.0 GT/s on RK3399 being unsafe

Or, if we'll go with the automatic downgrading, like this:

  PCI: rockchip: Limit RK3399 to Gen1 2.5 GT/s to prevent breakage