Re: rk3399 issue: no DMA in Linux with mainline TF-A and U-Boot SPL

From: Christoph Fritz <chf.fritz@googlemail.com>
To: "Russell King (Oracle)" <linux@armlinux.org.uk>,
	Kever Yang <kever.yang@rock-chips.com>
Cc: "U-Boot Mailing List" <u-boot@lists.denx.de>,
	"Quentin Schulz" <quentin.schulz@theobroma-systems.com>,
	"Heiko Stuebner" <heiko@sntech.de>,
	"Tony Xie" <tony.xie@rock-chips.com>,
	JuliusWerner <jwerner@chromium.org>,
	DanHandley <dan.handley@arm.com>,
	Rockchip <op-tee@rock-chips.com>,
	linux-arm-kernel@lists.infradead.org,
	op-tee@lists.trustedfirmware.org, tf-a@lists.trustedfirmware.org,
	张学广 <sugar.zhang@rock-chips.com>
Subject: Re: rk3399 issue: no DMA in Linux with mainline TF-A and U-Boot SPL
Date: Mon, 03 Apr 2023 15:50:47 +0200	[thread overview]
Message-ID: <874b4cc9c609fdb2bf13577b380560a66a2f7317.camel@googlemail.com> (raw)
In-Reply-To: <ZCrR+Vbhycm0TTel@shell.armlinux.org.uk>

On Mon, 2023-04-03 at 14:17 +0100, Russell King (Oracle) wrote:
> On Mon, Apr 03, 2023 at 12:11:40PM +0200, Christoph Fritz wrote:
> > > 
> > >      The ARM PL330 DMA driver in kernel only relate to:
> > > 
> > > - DTS kernel used, can be check in /proc/device-tree/
> > > 
> > > - kernel driver which should mach the compatible name.
> > 
> > drivers/dma/pl330.c needs also a successfully matched amba, but this
> > fails when using mainline TF-A and U-Boot SPL.
> > 
> > I'm using the same kernel and devicetree on both tests, the only thing
> > changed is TF-A and U-Boot SPL   vs   mini-loader and rk3399_bl31.
> > 
> > > This driver should has nothing to do with U-Boot SPL or TF-A, because we 
> > > don't have any special setting for PL330 in loader stage.
> > 
> > It is drivers/amba/bus.c, which is unable to find an AMBA_CID on the
> > ARM bus. The DMA driver not loading is just a symptom of this issue.
> 
> That brings up the obvious question: why is it unable to find the AMBA
> CID? Is that because some resource needed to read it hasn't been
> enabled yet?

That's my guess too, and that's why I'm asking Kever from Rockchip. To
me, it seems that their closed-source BL31 and/or mini-loader is
enabling something that is missing in upstream TF-A and/or U-Boot SPL.
On top of that, the registers responsible for that are undocumented.

But I could be wrong, and it's possible that I'm missing something
else. Maybe dumping the syscon-registers and comparing them might help,
but as far as I can see, it's a bit of an effort because they require
special treatment to be accessed.

>  If the AMBA CID is not accessible, presumably the rest of
> the PL330 also isn't accessible, so even if we could bind the driver,
> it still wouldn't work?

The PL330 driver attempted to probe, but was deferred due to a missing
AMBA_CID. It's in the bootlog that I attached in my first email in this
thread.

Thanks
  -- Christoph

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