On Fri, Aug 21, 2015 at 02:01:59AM +0300, Laurent Pinchart wrote: > > > How is 64 bit DMA addressing implemented ? Can you use a 64-bit VDMA on > > > a 32- bit platform with LPAE ? Can you use a 32-bit VDMA on a 64-bit > > > platform ? Given that VDMA is an IP core you can instantiate in the > > > programmable logic I expect some level of flexibility to be possible, but > > > this patch doesn't seem to support it. Please provide more context to > > > allow a proper review (and please include it in the commit message of v2). > > > > The VDMA core is a soft ip, which can be programmed to support both 32 bit > > and 64 bit addressing.When the VDMA core is configured for 32 bit address > > space , transfer start address is specified by a single register. > > > > When the VDMA core is configured for an address space greater than 32, each > > start address is specified by a combination of two registers.The first > > register specifies the LSB 32 bits of address, while the next register > > specifies the MSB 32 bits of address.For example,5Ch will specify the LSB > > bits while 60h will specify the MSB bits of the first start address. So we > > need to program two registers at a time. > > > > Yes,64 bit vdma can be used on 32 bit platform and 32 bit vdma can also be > > used on 64 bit platform.As far as i know , there is no use case where 64 > > bit dma can be used on 32 bit platform.Please correct me if i am wrong. > > I'm not sure what the use cases would be, but it makes me feel uncomfortable > to decide on whether the VDMA is 32 or 64 bits based on the type of CPU. > > As the VDMA flavour is selected at synthesis time, how about specifying it in > DT instead ? You could just add an address-width property. That would be saner thing to do. People wont check which IP and will mix and match. So you may have a 64 bit system with your 32 bit IP...
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