Re: [PATCH v1 2/2] block/nvme: Enable NVMe userspace driver for s390x

[Farhan Ali <alifm@linux.ibm.com>]

On 3/27/2025 12:26 PM, Stefan Hajnoczi wrote:
> On Wed, Mar 26, 2025 at 11:10:07AM -0700, Farhan Ali wrote:
>> +static inline uint32_t nvme_mmio_read_32(const void *addr)
>> +{
>> +    uint32_t ret;
>> +
>> +#ifdef __s390x__
>> +    ret = s390x_pci_mmio_read_32(addr);
>> +#else
>> +    /* Prevent the compiler from optimizing away the load */
>> +    ret = *((volatile uint32_t *)addr);
>> +#endif
> The NVMe driver should not need to worry about s390 PCI MMIO specifics.
> It would be nice to add a QEMU PCI MMIO load/store API that hides this.
>
> block/nvme.c would use the API to access MMIO registers instead of
> accessing them directly. The functions could be static inline in the
> header file to minimize overhead on platforms that can directly access
> PCI MMIO registers.

Hi Stefan,

Thanks for reviewing. I do agree, having a generic QEMU PCI MMIO 
load/store API for this would be good. And we can hide architecture 
specifics there. I didn't add that to begin with was NVMe driver would 
be the only place to consume it so thought might be unnecessary. I will 
refactor this in v2.

Thanks

Farhan