Re: [PATCH 4/5] iommu/mediatek: add support for mtk iommu generation one HW

[Robin Murphy <robin.murphy@arm.com>]

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

> +	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?

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

[...]

> +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...

> +	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;
> +}

[...]

> +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.