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Message-ID: <1463056884.29375.7.camel@mtksdaap41>
Date: Thu, 12 May 2016 20:41:24 +0800
From: Honghui Zhang <honghui.zhang@...iatek.com>
To: Robin Murphy <robin.murphy@....com>
CC: <joro@...tes.org>, <treding@...dia.com>, <mark.rutland@....com>,
<matthias.bgg@...il.com>, <catalin.marinas@....com>,
<will.deacon@....com>, <youlin.pei@...iatek.com>,
<yingjoe.chen@...iatek.com>, <devicetree@...r.kernel.org>,
<kendrick.hsu@...iatek.com>, <kernel@...gutronix.de>,
<arnd@...db.de>, <tfiga@...gle.com>, <robh+dt@...nel.org>,
<linux-mediatek@...ts.infradead.org>, <eddie.huang@...iatek.com>,
<linux-arm-kernel@...ts.infradead.org>, <pebolle@...cali.nl>,
<srv_heupstream@...iatek.com>, <erin.lo@...iatek.com>,
<linux-kernel@...r.kernel.org>, <iommu@...ts.linux-foundation.org>,
<djkurtz@...gle.com>, <p.zabel@...gutronix.de>,
<l.stach@...gutronix.de>
Subject: Re: [PATCH 4/5] iommu/mediatek: add support for mtk iommu
generation one HW
Hi, Robin, Thanks very much for your comment, and sorry for the last
reply format.
On Tue, 2016-05-10 at 11:28 +0100, Robin Murphy wrote:
> On 09/05/16 09:00, honghui.zhang@...iatek.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.
>
The dma_alloc_coheret interface is good enough for me, thanks.
> > + 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?
I will follow your advise for next version.
thanks.
>
> > + 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...
I would prefer your following advise to modify the pgsize_bitmap, thanks
very much.
>
> > + 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.
>
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