hi, Robin, thanks very much for your comments.

On 5/10/2016 6:28 PM, Robin Murphy wrote:

On 09/05/16 09:00, honghui.zhang@mediatek.com wrote:
[...]

quoted

+static void *mtk_iommu_alloc_pgt(struct device *dev, size_t size, gfp_t gfp)
+{
+    dma_addr_t dma;
+    void *pages = alloc_pages_exact(size, gfp | __GFP_ZERO);
+
+    if (!pages)
+        return NULL;
+
+    dma = dma_map_single(dev, pages, size, DMA_TO_DEVICE);
+    if (dma_mapping_error(dev, dma))
+        goto out_free;
+    /*
+     * We depend on the IOMMU being able to work with any physical
+     * address directly, so if the DMA layer suggests otherwise by
+     * translating or truncating them, that bodes very badly...
+     */
+    if (dma != virt_to_phys(pages))
+        goto out_unmap;

Given that you've only got a single table to allocate, and at 4MB it has a fair chance of failing beyond early boot time, just use dma_alloc_coherent() - you don't need to care about the dma <-> phys relationship because you don't have multi-level tables to walk. That way, you can get rid of all the awkward streaming DMA stuff, and also benefit from CMA to avoid allocation failures.

thanks, use dma_alloc_coherent is good for me.

quoted

+    kmemleak_ignore(pages);
+    return pages;
+
+out_unmap:
+    dev_err(dev, "Cannot accommodate DMA translation for IOMMU page tables\n");
+    dma_unmap_single(dev, dma, size, DMA_TO_DEVICE);
+out_free:
+    free_pages_exact(pages, size);
+    return NULL;
+
+}
+
+static void mtk_iommu_free_pgt(struct device *dev, void *pages, size_t size)
+{
+    dma_unmap_single(dev, (dma_addr_t)virt_to_phys(pages),
+             size, DMA_TO_DEVICE);
+    free_pages_exact(pages, size);
+}
+
+static int mtk_iommu_domain_finalise(struct mtk_iommu_data *data)
+{
+    struct mtk_iommu_domain *dom = data->m4u_dom;
+
+    spin_lock_init(&dom->pgtlock);
+
+    dom->pgt_va = mtk_iommu_alloc_pgt(data->dev,
+                dom->pgt_size, GFP_KERNEL);
+    if (!dom->pgt_va)
+        return -ENOMEM;
+
+    dom->pgt_pa = virt_to_phys(dom->pgt_va);
+
+    writel(dom->pgt_pa, data->base + REG_MMU_PT_BASE_ADDR);
+
+    dom->cookie = (void *)data;
+
+    return 0;
+}
+
+static struct iommu_domain *mtk_iommu_domain_alloc(unsigned type)
+{
+    struct mtk_iommu_domain *dom;
+
+    if (type != IOMMU_DOMAIN_UNMANAGED)
+        return NULL;
+
+    dom = kzalloc(sizeof(*dom), GFP_KERNEL);
+    if (!dom)
+        return NULL;
+
+    /*
+     * MTK m4u support 4GB iova address space, and oly support 4K page
+     * mapping. So the pagetable size should be exactly as 4M.
+     */
+    dom->pgt_size = SZ_4M;

If the table size is fixed, then why bother having a variable at all?

quoted

+    return &dom->domain;
+}
+
+static void mtk_iommu_domain_free(struct iommu_domain *domain)
+{
+    kfree(to_mtk_domain(domain));
+}
+

[...]

quoted

+static int mtk_iommu_map(struct iommu_domain *domain, unsigned long iova,
+             phys_addr_t paddr, size_t size, int prot)
+{
+    struct mtk_iommu_domain *dom = to_mtk_domain(domain);
+    struct mtk_iommu_data *data = dom->cookie;
+    unsigned int page_num = size >> MTK_IOMMU_PAGE_SHIFT;

Since you only advertise a single page size, this will always be 1, so you could either get rid of the loop here...

I would prefer your following advise to change the pgsize_bitmap. 
I would follow your advise in the next version.
Thanks very much.

quoted

+    unsigned long flags;
+    unsigned int i;
+    u32 *pgt_base_iova;
+    u32 pabase = (u32)paddr;
+    int map_size = 0;
+
+    spin_lock_irqsave(&dom->pgtlock, flags);
+    pgt_base_iova = dom->pgt_va + (iova  >> MTK_IOMMU_PAGE_SHIFT);
+    for (i = 0; i < page_num; i++) {
+        pgt_base_iova[i] = pabase | F_DESC_VALID | F_DESC_NONSEC;
+        pabase += MTK_IOMMU_PAGE_SIZE;
+        map_size += MTK_IOMMU_PAGE_SIZE;
+    }
+    dma_sync_single_for_device(data->dev,
+            dom->pgt_pa + (iova >> MTK_IOMMU_PAGE_SHIFT),
+            (size >> MTK_IOMMU_PAGE_SHIFT) * sizeof(u32),
+            DMA_TO_DEVICE);
+    spin_unlock_irqrestore(&dom->pgtlock, flags);
+
+    mtk_iommu_tlb_flush_range(data, iova, size);
+
+    return map_size;
+}

[...]

quoted

+static struct iommu_ops mtk_iommu_ops = {
+    .domain_alloc    = mtk_iommu_domain_alloc,
+    .domain_free    = mtk_iommu_domain_free,
+    .attach_dev    = mtk_iommu_attach_device,
+    .detach_dev    = mtk_iommu_detach_device,
+    .map        = mtk_iommu_map,
+    .unmap        = mtk_iommu_unmap,
+    .map_sg        = default_iommu_map_sg,
+    .iova_to_phys    = mtk_iommu_iova_to_phys,
+    .add_device    = mtk_iommu_add_device,
+    .remove_device    = mtk_iommu_remove_device,
+    .device_group    = mtk_iommu_device_group,
+    .pgsize_bitmap    = MTK_IOMMU_PAGE_SIZE,
+};

...or perhaps advertise .pgsize_bitmap = ~0UL << MTK_IOMMU_PAGE_SHIFT here, so you actually can handle multiple entries at once for larger mappings - given how simple the page table format is that doesn't seem too unreasonable, especially since it should give you a big efficiency win in terms of TLB maintenance.

Robin.