On Mon, 3 Jun 2019 14:09:02 +0200
Michael Mueller [off-list ref] wrote:

quoted

quoted

@@ -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,).
 */

quoted

quoted

+	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.
 */

Regards,
Halil