linux-kernel - Re: [PATCH 02/20] dma-mapping: provide a generic dma-noncoherent implementation

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Message-ID: <0c5d27e9-2799-eb38-8b09-47a04c48b5c7@gmx.de>
Date:   Fri, 18 May 2018 22:05:51 +0200
From:   Helge Deller <deller@....de>
To:     Alexey Brodkin <Alexey.Brodkin@...opsys.com>,
        "hch@....de" <hch@....de>
Cc:     "deanbo422@...il.com" <deanbo422@...il.com>,
        "linux-sh@...r.kernel.org" <linux-sh@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "nios2-dev@...ts.rocketboards.org" <nios2-dev@...ts.rocketboards.org>,
        "linux-m68k@...ts.linux-m68k.org" <linux-m68k@...ts.linux-m68k.org>,
        "linux-alpha@...r.kernel.org" <linux-alpha@...r.kernel.org>,
        "linux-hexagon@...r.kernel.org" <linux-hexagon@...r.kernel.org>,
        "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "green.hu@...il.com" <green.hu@...il.com>,
        "openrisc@...ts.librecores.org" <openrisc@...ts.librecores.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "monstr@...str.eu" <monstr@...str.eu>,
        "linux-parisc@...r.kernel.org" <linux-parisc@...r.kernel.org>,
        "linux-c6x-dev@...ux-c6x.org" <linux-c6x-dev@...ux-c6x.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "sparclinux@...r.kernel.org" <sparclinux@...r.kernel.org>,
        James Bottomley <James.Bottomley@...senPartnership.com>
Subject: Re: [PATCH 02/20] dma-mapping: provide a generic dma-noncoherent
 implementation

On 18.05.2018 15:03, Alexey Brodkin wrote:
> But the real fix of my problem is:
> ---------------------------------------->8------------------------------------
> --- a/lib/dma-noncoherent.c
> +++ b/lib/dma-noncoherent.c
> @@ -35,7 +35,7 @@ static dma_addr_t dma_noncoherent_map_page(struct device *dev, struct page *page
>  
>         addr = dma_direct_map_page(dev, page, offset, size, dir, attrs);
>         if (!dma_mapping_error(dev, addr) && !(attrs & DMA_ATTR_SKIP_CPU_SYNC))
> -               arch_sync_dma_for_device(dev, page_to_phys(page), size, dir);
> +               arch_sync_dma_for_device(dev, page_to_phys(page) + offset, size, dir);
>         return addr;
>  }
> ---------------------------------------->8------------------------------------
> 
> You seem to lost an offset in the page so if we happen to have a buffer not aligned to
> a page boundary then we were obviously corrupting data outside our data :)

Good.
This patch seems to fix the dma issues I faced on my 32bit B160L parisc box.

So it leaves only one open issue on parisc:
Now every 32 bit parisc system is unnecessarily non-coherent.

Helge