Re: [PATCH v2 02/15] NTB: Set dma mask and dma coherent mask to NTB devices

[Logan Gunthorpe]

On 05/12/17 09:51 AM, Jon Mason wrote:
> On Sun, Dec 3, 2017 at 2:17 PM, Serge Semin <fancer.lancer@xxxxxxxxx> wrote:
> > The dma_mask and dma_coherent_mask fields of the NTB struct device
> > weren't initialized in hardware drivers. In fact it should be done
> > instead of PCIe interface usage, since NTB clients are supposed to
> > use NTB API only and left unaware of real hardware implementation.
> > In addition to that ntb_device_register() method shouldn't clear
> > the passed ntb_dev structure, since it dma_mask is initialized
> > by hardware drivers.
>
> This seems like a bug fix.  Should this be broken out of this patch or
> is it not noticed without your changes?

I was digging into this a bit more and in addition to my earlier review 
comments I think the patch is incorrect for a couple reasons:

1) dma_set_mask() (and friends) are meant to inform the kernel of device 
specific restrictions it cannot know. Calling it with the parent PCI 
device's mask seems pointless.

2) Every dma_alloc() call in the NTB subsystem uses the PCI device's 
struct device. This is ugly in itself but until it changes this patch 
does nothing.

Logan