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_arm. > > c > > b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm. > > c > > index a5afcc5..6fa2b5a 100644 > > --- > > a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm. > > c > > +++ > > b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm. > > 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. _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
