Re: [Qemu-devel] [PATCH] hw/riscv/virt: re-add machine-specific compatible string to /soc/ node

[Auer, Lukas]

Hi Bin,

On Wed, 2019-03-13 at 09:51 +0800, Bin Meng wrote:
> Hi Lukas,
> 
> On Tue, Mar 12, 2019 at 10:39 PM Auer, Lukas
> <address@hidden> wrote:
> > Hi Bin,
> > 
> > On Mon, 2019-03-11 at 23:28 +0800, Bin Meng wrote:
> > > Hi Lukas,
> > > 
> > > On Mon, Mar 11, 2019 at 2:03 AM Auer, Lukas
> > > <address@hidden> wrote:
> > > > Hi Bin,
> > > > 
> > > > On Sun, 2019-03-10 at 22:57 +0800, Bin Meng wrote:
> > > > > Hi Lukas,
> > > > > 
> > > > > On Sun, Mar 10, 2019 at 9:44 PM Auer, Lukas
> > > > > <address@hidden> wrote:
> > > > > > Hi Bin,
> > > > > > 
> > > > > > On Sun, 2019-03-10 at 09:07 +0800, Bin Meng wrote:
> > > > > > > Hi Lukas,
> > > > > > > 
> > > > > > > On Mon, Feb 11, 2019 at 6:13 AM Lukas Auer
> > > > > > > <address@hidden> wrote:
> > > > > > > > Re-add the previous compatible string "riscv-virtio-
> > > > > > > > soc" to
> > > > > > > > the
> > > > > > > > soc
> > > > > > > > device tree node to allow U-Boot and Linux to bind
> > > > > > > > machine-
> > > > > > > > specific
> > > > > > > > drivers to it. The current compatible string "simple-
> > > > > > > > bus"
> > > > > > > > is
> > > > > > > > retained.
> > > > > > > > 
> > > > > > > > This is required by U-Boot to bind devices early, as
> > > > > > > > part
> > > > > > > > of
> > > > > > > > the
> > > > > > > > pre-relocation driver model.
> > > > > > > > 
> > > > > > > 
> > > > > > > I see no problem with U-Boot working with current
> > > > > > > compatible
> > > > > > > string
> > > > > > > "simple-bus". In fact I had planned to remove the
> > > > > > > compatible
> > > > > > > string
> > > > > > > "riscv-virtio-soc" in U-Boot but did not get time to work
> > > > > > > on
> > > > > > > it.
> > > > > > > 
> > > > > > 
> > > > > > It is only required if U-Boot is running in machine-mode.
> > > > > > For
> > > > > > relocation it needs to use the CLINT driver to send
> > > > > > appropriate
> > > > > > IPIs to
> > > > > > the other harts. To be able to probe the driver, the device
> > > > > > and
> > > > > > its
> > > > > > parent device tree node (soc) must therefore be available
> > > > > > in
> > > > > > the
> > > > > > pre-
> > > > > > relocation device model.
> > > > > > This patch was the easiest way I could think of for
> > > > > > achieving
> > > > > > this.
> > > > > > It
> > > > > > could be that there is a better way of solving this.
> > > > > > 
> > > > > 
> > > > > I tested your SMP U-Boot series in both M-mode and S-mode,
> > > > > using
> > > > > a 4
> > > > > core 'virt' target. Works fine. I am using QEMU 3.1.0 so it
> > > > > is
> > > > > "simple-bus".
> > > > > 
> > > > 
> > > > That is actually my fault, it should not work.
> > > > What is happening is that U-Boot fails to relocate the
> > > > secondary
> > > > harts,
> > > > because the CLINT driver cannot get the memory address of the
> > > > CLINT
> > > > device. This error is currently silently ignored.
> > > 
> > > I still don't understand. Why does the CLINT driver fail to get
> > > the
> > > memory address? U-Boot has been supporting "simpile-bus" for a
> > > long
> > > time. It was because QEMU 3.0.0 generated the /soc node with
> > > "riscv-virtio-soc" compatible string, U-Boot was taught to treat
> > > such
> > > compatible string as a "simple-bus" too (that was the U-Boot
> > > commit
> > > 27dc2c130e29)
> > 
> > That's correct. The problem with the default simple-bus U-Boot
> > driver
> > is that it does not have the DM_FLAG_PRE_RELOC flag set. The /soc
> > and
> > /soc/clint nodes are therefore not available before relocation,
> > meaning
> > that IPIs cannot be sent to relocate the secondary harts.
> > 
> 
> Thanks for the clarifications. Now I see the problem. But I think we
> should fix U-Boot "simple-bus" driver instead. As seen on FU540 or
> likely other hardware, QEMU generates the "simple-bus" compatible
> string for the /soc node, as well as the DT provided by the hardware.
> 

That makes sense, I can send a patch to set the DM_FLAG_PRE_RELOC flag
in the simple-bus U-Boot driver. I think it's best to send it
separately from the SMP patch series, since it could affect other
boards and it's a bit late in the release cycle. What do you think?

This patch can be dropped then.

Thanks,
Lukas