> -----Original Message----- > From: Wolfgang Denk [mailto:[email protected]] > Sent: Monday, July 23, 2012 11:18 AM > To: Aggrwal Poonam-B10812 > Cc: Marek Vasut; [email protected]; [email protected] > Subject: Re: Forcing PIO mode instead of DMA via DT property > > Dear Poonam, > > In message <ACB6D0C0104CFF42A45A5D82A0DD4F3D079B4DAE@039-SN2MPN1- > 013.039d.mgd.msft.net> you wrote: > > > > > I'm trying to implement a driver that can do both DMA and PIO, and > > > it would be nice if the user was able to select the mode (on a > > > per-bus > > > basis) using the DT. > > > The PIO mode can reduce the overhead in some cases and therefore be > > > better choice than the DMA (for example when most transfers move > > > only very few data, or when board-specific hardware properties kick > in). > > > > > > I was thinking about using some "manf,use-pio" DT property, but I > > > haven't found any such example yet, so I wonder if this is a good > idea. > > Not sure, but as far as I understand device tree is to publish the > > hardware capabilities, not the user choice/configuration. > > One option would be to put a compile time flag in the driver, which > > prefers PIO than DMA. > > I believe by default DMA is the first preference. > > We just had such a situation, where PIO had to be used on a specific bus, > because due to a hardware problem (board design error) DMA would crash > the system. Yet the same driver/kernel would work fine with DMA on other > buses / boards. OK, this was on x86, so DT would not have helped, but I > think a bus-specific property of being able to do DMA (or not) might > indeed make sense for the DT. In that case probably we can use QUIRKS like broken-dma. I see this in the sdhc driver in Linux. On P2020 chip(rev 1.0) of FSL DMA was broken so we used this to force PIO.
Regards Poonam > > Best regards, > > Wolfgang Denk > > -- > DENX Software Engineering GmbH, MD: Wolfgang Denk & Detlev Zundel > HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany > Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: [email protected] "I > haven't lost my mind - it's backed up on tape somewhere." _______________________________________________ devicetree-discuss mailing list [email protected] https://lists.ozlabs.org/listinfo/devicetree-discuss
