From mboxrd@z Thu Jan 1 00:00:00 1970 From: Valentine Date: Wed, 29 Jan 2014 12:47:56 +0000 Subject: Re: [PATCH RFC 0/2] ARM: shmobile: lager: Enable DMA bounce for PCI Message-Id: <52E8F87C.1070101@cogentembedded.com> List-Id: References: <1390935213-12896-1-git-send-email-valentine.barshak@cogentembedded.com> In-Reply-To: <1390935213-12896-1-git-send-email-valentine.barshak@cogentembedded.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-sh@vger.kernel.org On 01/29/2014 04:45 PM, Ben Dooks wrote: > On 29/01/14 11:15, Valentine wrote: >> On 01/29/2014 12:03 PM, Ben Dooks wrote: >>> On 29/01/14 06:45, Simon Horman wrote: >>>> On Tue, Jan 28, 2014 at 10:53:31PM +0400, Valentine Barshak wrote: >>>>> This enables DMA bounce for PCI since the controller does >>>>> not support more than 2G PCI-AHB memory window. >>>>> The problems with DMA transfers can be observed when >>>>> setting 2G/2G user/kernel memory split model >>>>> (CONFIG_VMSPLIT_2G=y) >>>>> These patches help to avoid it. >>>> >>>> Are these patches compatible with other user/kernel splits? >>> >>> PS, the bridge is only actually capable of seeing 1GiB of >>> RAM due to alignment issues in the window. You can have either >>> 0x4..0x8 or 0x8..0xc but not /both/. If you open the window to >>> 2GiB then you can see either 0x0..0x8 or 0x8..0xF range. >>> >> >> I don't think this is relater to the user/kernel space memory split. >> >> Currently the R-Car Gen2 PCI driver uses 0x40000000 - 0x7fffffff >> PCI-AHB region. We can set it to 0x00000000 - 0x7fffffff, >> but there's no RAM below 0x40000000 so no DMA access to that area is >> actually legal from the PCI USB host driver. >> So the change wouldn't give us much. > > Well, there's IO areas but probably not wanting to DMA to them anyway. > >> The 31-bit DMA mask takes care of forbidding any DMA transfers >> to the area above 0x7fffffff. > > I will add this to our current patch series and see if it helps. Helps with what? I don't see any issues with the current patches. Thanks, Val.