Re: [PATCH 18/21] scsi: sd: Support reading atomic properties from block limits VPD

[John Garry]

On 29/09/2023 18:54, Bart Van Assche wrote:
> On 9/29/23 03:27, John Garry wrote:
> > +static void sd_config_atomic(struct scsi_disk *sdkp)
> > +{
> > +    unsigned int logical_block_size = sdkp->device->sector_size;
> > +    struct request_queue *q = sdkp->disk->queue;
> > +
> > +    if (sdkp->max_atomic) {
>
> Please use the "return early" style here to keep the indentation
> level in this function low.

ok, fine.

> > +        unsigned int max_atomic = max_t(unsigned int,
> > +            rounddown_pow_of_two(sdkp->max_atomic),
> > +            rounddown_pow_of_two(sdkp->max_atomic_with_boundary));
> > +        unsigned int unit_min = sdkp->atomic_granularity ?
> > +            rounddown_pow_of_two(sdkp->atomic_granularity) :
> > +            physical_block_size_sectors;
> > +        unsigned int unit_max = max_atomic;
> > +
> > +        if (sdkp->max_atomic_boundary)
> > +            unit_max = min_t(unsigned int, unit_max,
> > +                rounddown_pow_of_two(sdkp->max_atomic_boundary));
>
> Why does "rounddown_pow_of_two()" occur in the above code?

I assume that you are talking about all the code above to calculate 
atomic write values for the device.

The reason is that atomic write unit min and max are always a power-of-2 
- see rules described earlier - as so that we why we rounddown to a 
power-of-2.

Thanks,
John