drm/verisilicon: properly implement vmap

[Icenowy]

On 6.6 kernel, the address returned by dma_alloc_attrs() is directly from the linear mapping and not mapped with the expected page attribute.

Properly implement a vmap (and corresponding vunmap) to ensure the virtual address set by it is mapped with the expect write-combining page attributes.

===============

This PR fixes fbcon refreshing issue on (at least) Lichee Console 4A.

Summary by Sourcery

Apply proper vmap/vunmap mapping with write-combining attributes for Verisilicon GEM objects to ensure correct kernel mappings and resolve framebuffer refresh issues.

Bug Fixes:

• Fix fbcon refreshing issue on Lichee Console 4A by ensuring memory is mapped with write-combining attributes

Enhancements:

• Implement vmap() in vs_gem_prime_vmap with pgprot_writecombine and corresponding vunmap() in vs_gem_prime_vunmap
• Add a new vaddr field to vs_gem_object to track the virtual mapping
• Replace legacy direct kernel mapping of dma_alloc_attrs() return values to guarantee correct page attributes

[sourcery-ai]

Reviewer's Guide

This PR replaces direct linear DMA mappings with explicit vmap/vunmap calls to ensure write-combining page attributes by adding a vaddr field for tracking and updating both prime_vmap and prime_vunmap implementations.

Class diagram for updated vs_gem_object and vmap/vunmap logic

classDiagram
    class vs_gem_object {
        drm_gem_object base
        size_t size
        void *cookie
        void *vaddr
        dma_addr_t dma_addr
        u32 iova
        unsigned long dma_attrs
    }

    class vs_gem_prime_vmap {
        +int vs_gem_prime_vmap(drm_gem_object *obj, iosys_map *map)
    }
    class vs_gem_prime_vunmap {
        +void vs_gem_prime_vunmap(drm_gem_object *obj, iosys_map *map)
    }

    vs_gem_object <.. vs_gem_prime_vmap : uses
    vs_gem_object <.. vs_gem_prime_vunmap : uses

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Flow diagram for vmap/vunmap implementation in vs_gem_prime_vmap/vunmap

flowchart TD
    A[vs_gem_prime_vmap called] --> B{vs_obj->vaddr exists?}
    B -- Yes --> C[Set iosys_map to vs_obj->vaddr]
    B -- No --> D[Calculate nr_pages]
    D --> E[Call vmap with write-combining attributes]
    E --> F{vmap success?}
    F -- Yes --> G[Set vs_obj->vaddr]
    F -- No --> H[Return -ENOMEM]
    G --> C
    C --> I[Return 0]

    subgraph Unmapping
      J[vs_gem_prime_vunmap called] --> K{vs_obj->vaddr exists?}
      K -- No --> L[Return]
      K -- Yes --> M[Call vunmap on vs_obj->vaddr]
      M --> N[Set vs_obj->vaddr to NULL]
    end

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File-Level Changes

Change	Details	Files
Track and store virtual mapping address	Add vaddr field to struct vs_gem_object to hold vmap result	drivers/gpu/drm/verisilicon/vs_gem.h
Implement vmap in prime_vmap	Calculate number of pages from object size Call vmap with pgprot_writecombine and store in vaddr Add reuse path for existing vaddr Handle allocation failure and return -ENOMEM Replace conditional cookie-based mapping logic	drivers/gpu/drm/verisilicon/vs_gem.c
Implement vunmap in prime_vunmap	Check if vaddr is set before unmapping Call vunmap on vaddr and clear vaddr field	drivers/gpu/drm/verisilicon/vs_gem.c

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[sourcery-ai]

Hey @Icenowy - I've reviewed your changes and they look great!

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[Icenowy]

Superseded by #31 .