Re: [PATCH v5 for-next 1/1] RDMA/hns: Support direct wqe of userspace'

[Barry Song <21cnbao@gmail.com>]

> +	switch (entry->mmap_type) {
> +	case HNS_ROCE_MMAP_TYPE_DB:
> +		prot = pgprot_noncached(vma->vm_page_prot);
> +		break;
> +	case HNS_ROCE_MMAP_TYPE_TPTR:
> +		prot = vma->vm_page_prot;
> +		break;
> +	/*
> +	 * The BAR region of direct WQE supports Early Write Ack,
> +	 * so pgprot_device is used to improve performance.
> +	 */
> +	case HNS_ROCE_MMAP_TYPE_DWQE:
> +		prot = pgprot_device(vma->vm_page_prot);
> +		break;
> +	default:
> +		return -EINVAL;
> +	}

i am still not convinced why HNS_ROCE_MMAP_TYPE_DB needs nocache and HNS_ROCE_MMAP_TYPE_DWQE needs
device. generally people use ioremap() to map pci bar spaces in pci device drivers, and ioremap()
is pretty much nGnRE:
#define ioremap(addr, size)             __ioremap((addr), (size), __pgprot(PROT_DEVICE_nGnRE))
#define ioremap_np(addr, size)          __ioremap((addr), (size), __pgprot(PROT_DEVICE_nGnRnE))

i am only seeing four places which are using nE in kernel:
   #   line  filename / context / line
   1    866  drivers/of/address.c <<of_iomap>>
             return ioremap_np(res.start, resource_size(&res));
   2    901  drivers/of/address.c <<of_io_request_and_map>>
             mem = ioremap_np(res.start, resource_size(&res));
   3     89  include/linux/io.h <<pci_remap_cfgspace>>
             return ioremap_np(offset, size) ?: ioremap(offset, size);
   4     47  lib/devres.c <<__devm_ioremap>>
             addr = ioremap_np(offset, size);

so i guess nGnRE is quite safe for pci device bar spaces. for config space, it is a different story
though which is the 3rd one in the above list:

#ifdef CONFIG_PCI
/*
 * The PCI specifications (Rev 3.0, 3.2.5 "Transaction Ordering and
 * Posting") mandate non-posted configuration transactions. This default
 * implementation attempts to use the ioremap_np() API to provide this
 * on arches that support it, and falls back to ioremap() on those that
 * don't. Overriding this function is deprecated; arches that properly
 * support non-posted accesses should implement ioremap_np() instead, which
 * this default implementation can then use to return mappings compliant with
 * the PCI specification.
 */
#ifndef pci_remap_cfgspace
#define pci_remap_cfgspace pci_remap_cfgspace
static inline void __iomem *pci_remap_cfgspace(phys_addr_t offset,
                                               size_t size)
{
        return ioremap_np(offset, size) ?: ioremap(offset, size);
}
#endif
#endif

Thanks
Barry