linux-kernel - Re: [PATCH 6/7] drm/etnaviv: add shared context support for iommuv2

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Message-ID: <05ef7c0df0a2235277030b9e33f34082e8938faa.camel@icenowy.me>
Date: Tue, 02 Sep 2025 23:40:02 +0800
From: Icenowy Zheng <uwu@...nowy.me>
To: Drew Fustini <fustini@...nel.org>, Guo Ren <guoren@...nel.org>, Fu Wei
 <wefu@...hat.com>, Lucas Stach <l.stach@...gutronix.de>, Russell King
 <linux+etnaviv@...linux.org.uk>, Christian Gmeiner
 <christian.gmeiner@...il.com>,  David Airlie <airlied@...il.com>, Simona
 Vetter <simona@...ll.ch>
Cc: linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	etnaviv@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH 6/7] drm/etnaviv: add shared context support for iommuv2

在 2025-08-16星期六的 15:47 +0800，Icenowy Zheng写道：
> Unfortunately the GC620 GPU seems to have broken PTA capibility, and
> switching page table ID in command stream after it's running won't
> work.
> As directly switching mtlb isn't working either, there will be no
> reliable way to switch page table in the command stream, and a shared
> context, like iommuv1, is needed.
> 
> Add support for this shared context situation. Shared context is set
> when the broken PTA is known, and the context allocation code will be
> made short circuit when a shared context is set.
> 
> Signed-off-by: Icenowy Zheng <uwu@...nowy.me>
> ---
>  drivers/gpu/drm/etnaviv/etnaviv_iommu_v2.c | 8 ++++++++
>  drivers/gpu/drm/etnaviv/etnaviv_mmu.c      | 1 +
>  drivers/gpu/drm/etnaviv/etnaviv_mmu.h      | 2 ++
>  3 files changed, 11 insertions(+)
> 
> diff --git a/drivers/gpu/drm/etnaviv/etnaviv_iommu_v2.c
> b/drivers/gpu/drm/etnaviv/etnaviv_iommu_v2.c
> index 5654a604c70cf..960ba3d659dc5 100644
> --- a/drivers/gpu/drm/etnaviv/etnaviv_iommu_v2.c
> +++ b/drivers/gpu/drm/etnaviv/etnaviv_iommu_v2.c

Well, I forgot to clean shared_context in etnaviv_iommuv2_free() when
the shared context is torn down...

> @@ -273,6 +273,12 @@ etnaviv_iommuv2_context_alloc(struct
> etnaviv_iommu_global *global)
>         struct etnaviv_iommu_context *context;
>  
>         mutex_lock(&global->lock);
> +       if (global->shared_context) {
> +               context = global->shared_context;
> +               etnaviv_iommu_context_get(context);
> +               mutex_unlock(&global->lock);
> +               return context;
> +       }
>  
>         v2_context = vzalloc(sizeof(*v2_context));
>         if (!v2_context)
> @@ -301,6 +307,8 @@ etnaviv_iommuv2_context_alloc(struct
> etnaviv_iommu_global *global)
>         mutex_init(&context->lock);
>         INIT_LIST_HEAD(&context->mappings);
>         drm_mm_init(&context->mm, SZ_4K, (u64)SZ_1G * 4 - SZ_4K);
> +       if (global->v2.broken_pta)
> +               global->shared_context = context;
>  
>         mutex_unlock(&global->lock);
>         return context;
> diff --git a/drivers/gpu/drm/etnaviv/etnaviv_mmu.c
> b/drivers/gpu/drm/etnaviv/etnaviv_mmu.c
> index df5192083b201..a0f9c950504e0 100644
> --- a/drivers/gpu/drm/etnaviv/etnaviv_mmu.c
> +++ b/drivers/gpu/drm/etnaviv/etnaviv_mmu.c
> @@ -504,6 +504,7 @@ int etnaviv_iommu_global_init(struct etnaviv_gpu
> *gpu)
>         memset32(global->bad_page_cpu, 0xdead55aa, SZ_4K /
> sizeof(u32));
>  
>         if (version == ETNAVIV_IOMMU_V2) {
> +               global->v2.broken_pta = gpu->identity.model ==
> chipModel_GC620;
>                 global->v2.pta_cpu = dma_alloc_wc(dev,
> ETNAVIV_PTA_SIZE,
>                                                &global->v2.pta_dma,
> GFP_KERNEL);
>                 if (!global->v2.pta_cpu)
> diff --git a/drivers/gpu/drm/etnaviv/etnaviv_mmu.h
> b/drivers/gpu/drm/etnaviv/etnaviv_mmu.h
> index 2ec4acda02bc6..5627d2a0d0237 100644
> --- a/drivers/gpu/drm/etnaviv/etnaviv_mmu.h
> +++ b/drivers/gpu/drm/etnaviv/etnaviv_mmu.h
> @@ -55,6 +55,8 @@ struct etnaviv_iommu_global {
>                 u64 *pta_cpu;
>                 dma_addr_t pta_dma;
>                 DECLARE_BITMAP(pta_alloc, ETNAVIV_PTA_ENTRIES);
> +               /* Whether runtime switching page table ID will fail
> */
> +               bool broken_pta;
>         } v2;
>  };
>