On Mon, 2016-10-31 at 12:53 -0700, Michael Zoran wrote: > On Mon, 2016-10-31 at 11:40 -0700, Michael Zoran wrote: > > On Mon, 2016-10-31 at 11:36 -0700, Eric Anholt wrote: > > > Michael Zoran <mzoran@xxxxxxxxxxxx> writes: > > > > > > > Setting the DMA mask is optional on 32 bit but > > > > is mandatory on 64 bit. Set the DMA mask and coherent > > > > to force all DMA to be in the 32 bit address space. > > > > > > > > This is considered a "good practice" and most drivers > > > > already do this. > > > > > > > > Signed-off-by: Michael Zoran <mzoran@xxxxxxxxxxxx> > > > > --- > > > > .../staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c > > > > | > > > > 10 ++++++++++ > > > > 1 file changed, 10 insertions(+) > > > > > > > > diff --git > > > > a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_ > > > > ar > > > > m. > > > > c > > > > b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_ > > > > ar > > > > m. > > > > c > > > > index a5afcc5..6fa2b5a 100644 > > > > --- > > > > a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_ > > > > ar > > > > m. > > > > c > > > > +++ > > > > b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_ > > > > ar > > > > m. > > > > c > > > > @@ -97,6 +97,16 @@ int vchiq_platform_init(struct > > > > platform_device > > > > *pdev, VCHIQ_STATE_T *state) > > > > int slot_mem_size, frag_mem_size; > > > > int err, irq, i; > > > > > > > > + /* > > > > + * Setting the DMA mask is necessary in the 64 bit > > > > environment. > > > > + * It isn't necessary in a 32 bit environment but is > > > > considered > > > > + * a good practice. > > > > + */ > > > > + err = dma_set_mask_and_coherent(dev, > > > > DMA_BIT_MASK(32)); > > > > > > I think a better comment here would be simply: > > > > > > /* VCHI messages between the CPU and firmware use 32-bit bus > > > addresses. */ > > > > > > explaining why the value is chosen (once you know that the 32 bit > > > restriction exists, reporting it is obviously needed). I'm > > > curious, > > > though: what failed when you didn't set it? > > > > > > > The comment is easy to change. > > > > I don't have the log available ATM, but if I remember the DMA API's > > bugcheck the first time that are used. > > > > I think this was a policy decision or something because the > > information > > should be available in the dma-ranges. > > > > If it's important, I can setup a test again without the change and > > e- > > mail the logs. > > > > If you look at the DWC2 driver you will see that it also sets this > > mask. > > OK, I'm begging to understand this. It appears the architecture > specific paths are very different. > > In arm the mask and coherent is set to DMA_BIT_MASK(32) in mm/dma- > mapping.c the first time the dma APIs are used. On arm64, it appears > this variable is uninitialized and will contain random crude. > > Like I said, I don't know if this is a policy decision or if it just > slipped through the cracks. > Actually, I'm getting confused here. If I need to prove this is needed, is their anybody I can send e-mail to that has a deep understanding of the two different architecture paths. Perhaps they can explain exactly why arm64 is not defaulting to 32 bit DMA. _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
