On Mon, Sep 01, 2025 at 11:47:59PM +0200, Marek Szyprowski wrote:
> I would like to give those patches a try in linux-next, but in meantime
> I tested it on my test farm and found a regression in dma_map_resource()
> handling. Namely the dma_map_resource() is no longer possible with size
> not aligned to kmalloc()'ed buffer, as dma_direct_map_phys() calls
> dma_kmalloc_needs_bounce(),
Hmm, it's this bit:
capable = dma_capable(dev, dma_addr, size, !(attrs & DMA_ATTR_MMIO));
if (unlikely(!capable) || dma_kmalloc_needs_bounce(dev, size, dir)) {
if (is_swiotlb_active(dev) && !(attrs & DMA_ATTR_MMIO))
return swiotlb_map(dev, phys, size, dir, attrs);
goto err_overflow;
}
We shouldn't be checking dma_kmalloc_needs_bounce() on mmio as there
is no cache flushing so the "dma safe alignment" for non-coherent DMA
does not apply.
Like you say looks good to me, and more of the surrouding code can be
pulled in too, no sense in repeating the boolean logic:
if (attrs & DMA_ATTR_MMIO) {
dma_addr = phys;
if (unlikely(!dma_capable(dev, dma_addr, size, false)))
goto err_overflow;
} else {
dma_addr = phys_to_dma(dev, phys);
if (unlikely(!dma_capable(dev, dma_addr, size, true)) ||
dma_kmalloc_needs_bounce(dev, size, dir)) {
if (is_swiotlb_active(dev))
return swiotlb_map(dev, phys, size, dir, attrs);
goto err_overflow;
}
if (!dev_is_dma_coherent(dev) &&
!(attrs & DMA_ATTR_SKIP_CPU_SYNC))
arch_sync_dma_for_device(phys, size, dir);
}
Jason
