Re: [PATCH v3 2/8] s390/cio: introduce DMA pools to cio

[Cornelia Huck <cohuck@redhat.com>]

On Mon, 3 Jun 2019 14:57:30 +0200
Halil Pasic <pasic@linux.ibm.com> wrote:

> On Mon, 3 Jun 2019 14:09:02 +0200
> Michael Mueller <mimu@linux.ibm.com> wrote:
> 
> > >> @@ -224,6 +226,8 @@ struct subchannel *css_alloc_subchannel(struct subchannel_id schid,
> > >>   	INIT_WORK(&sch->todo_work, css_sch_todo);
> > >>   	sch->dev.release = &css_subchannel_release;
> > >>   	device_initialize(&sch->dev);    
> > > 
> > > It might be helpful to add a comment why you use 31 bit here...    
> > 
> > @Halil, please let me know what comment you prefere here...
> >   
> 
> How about?
> 
> /*
>  * The physical addresses of some the dma structures that
>  * can belong  to a subchannel need to fit 31 bit width (examples ccw,).
>  */

"e.g. ccw"?

> 
> 
> > >     
> > >> +	sch->dev.coherent_dma_mask = DMA_BIT_MASK(31);
> > >> +	sch->dev.dma_mask = &sch->dev.coherent_dma_mask;
> > >>   	return sch;
> > >>   
> > >>   err:
> > >> @@ -899,6 +903,8 @@ static int __init setup_css(int nr)
> > >>   	dev_set_name(&css->device, "css%x", nr);
> > >>   	css->device.groups = cssdev_attr_groups;
> > >>   	css->device.release = channel_subsystem_release;    
> > > 
> > > ...and 64 bit here.    
> > 
> > and here.  
> 
> /*
>  * We currently allocate notifier bits with this (using css->device
>  * as the device argument with the DMA API), and are fine with 64 bit
>  * addresses.
>  */

Thanks, that makes things hopefully clearer if we look at it some time
in the future ;)