Re: [PATCH] drm: verisilicon: support non-coherent DMA framebuffers

[Dominique Belhachemi]

On Tue, Sep 29, 2026 at 3:27 AM Icenowy Zheng <zhengxingda@xxxxxxxxxxx> wrote:
>
> 在 2026-09-28一的 01:21 -0400，Dominique Belhachemi写道：
> > On Fri, Sep 11, 2026 at 11:33 AM Icenowy Zheng
> > <zhengxingda@xxxxxxxxxxx> wrote:
> > >
> > > I am still thinking how to decide whether to use dirty-tracking-
> > > based
> > > cache coherent maintenance or writecombine/uncached mapping.
> > >
> > Hi Icenowy,
> >
> > I looked into this again and writecombine/uncached mapping is the way
> > to go.
>
> I think drm/imagination really requires it (because the correspoding
> userspace driver advertises only one memory type with
> `HOST_COHERENT_BIT` set), however in the future it could also add cache
> maintenance support for performance reasons.
>
> > I used Bo Gan's XPbmtUC series and Michal Wilczynski's jh7110 display
> > series and finally got the integrated BXE-4-32 GPU to work.
>
> The XPbmtUC series is problematic -- it "supports EIC7700" "with a
> hypervisor", which means it cannot run on EIC7700 natively. This
> severely restricts its usage.
>
> Samuel Holland from SiFive is working on patching the PTE on-the-fly,
> but that will change all code accessing PTE in the kernel and thus is a
> heavy work.
>
> P.S. For the JH7110 rascal+dust power issue, I did a try-and-error hack
> at [1]. The basical register definition of this register (called
> RGX_CR_POWER_EVENT) is available in their KM volcanic part (but it
> seems to apply for rogue too), but the individual bits for domains are
> undocumented, and the highest 8-bit seems to be some kind of multi-core
> mask on Rogue.
>
>
> [1]
> https://github.com/Icenowy/linux/commit/09db317c9c229ef359e35463f8c08efd3e23c685
>
Wow, thanks for sharing this. It works reliably and helped me get rid
of the double-insmod for powervr.
I integrated it into my branch with updated #defines.

Best
-Dominique

> >
> > https://lore.kernel.org/all/20260316060328.1173634-1-ganboing@xxxxxxxxx/
> > https://lore.kernel.org/all/20260915-jh7110-clean-send-v4-0-f0e4fd6f2cc8@xxxxxxxxxxx/
> > https://github.com/domibel/visionfive2_gpu_bringup
> >