RE: [PATCH v2] udmabuf: respect the device's maximum segment size

[Kasireddy, Vivek]

Hi Karl,

> Subject: Re: [PATCH v2] udmabuf: respect the device's maximum
> segment size
> 
> On Tue, Sep 29, 2026 at 07:48:35AM +0100, Karl Mehltretter wrote:
> > get_sg_table() merges physically contiguous pages without accounting
> > for the mapping device's maximum segment size. This affects both
> > importer mappings and the udmabuf misc device mapping used for
> CPU
> > access.
> >
> > With DMA_API_DEBUG enabled, DMA_BUF_IOCTL_SYNC on a 64 MiB
> udmabuf
> > reports:
> >
> >   DMA-API: misc udmabuf: mapping sg segment longer than device
> claims to
> >   support [len=65884160] [max=65536]
> >
> > Use sg_alloc_table_from_pages_segment() with the mapping device's
> > maximum segment size. Return -EINVAL if the limit is smaller than
> > PAGE_SIZE because the page-based allocator cannot honor it.
> >
> > Before commit 5bf888673e0d ("udmabuf: Do not create malformed
> > scatterlists"), each entry covered one page.
> >
> > Fixes: 5bf888673e0d ("udmabuf: Do not create malformed
> scatterlists")
> > Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
> > Assisted-by: LLM
> > Signed-off-by: Karl Mehltretter <kmehltretter@xxxxxxxxx>
> 
> Friendly ping on v2. It has Reviewed-by tags from Jason and Christian.
Will push this patch to drm-misc-next soon (in a day or two).

Thanks,
Vivek

> 
> Thanks,
> Karl