Re: [RFC] libata-scsi: make sure Maximum Write Same Length is not too large

On Fri, Aug 12, 2016 at 3:56 PM, Martin K. Petersen
[off-list ref] wrote:

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"Tom" == Tom Yan [off-list ref] writes:

Tom,

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put_unaligned_be64(65535 * ATA_MAX_TRIM_RNUM / (sector_size / 512), &rbuf[36]);

How many 8-byte ranges fit in a 4096-byte sector?

Tom> So were you trying to pointing out something I am still missing, or
Tom> were you merely confirming I was right?

I suggest you drop ATA_MAX_TRIM_RNUM and do:

enum {
     ATA_TRIM_BLOCKS_PER_RANGE = 65535, /* 0xffff blocks per range desc. */
     ATA_TRIM_RANGE_SIZE_SHIFT = 3,     /* range descriptor is 8 bytes */
};

put_unaligned_be64(ATA_TRIM_BLOCKS_PER_RANGE *
                   sector_size >> ATA_TRIM_RANGE_SIZE_SHIFT, &rbuf[36]);

Might be worthwhile to create an ata_max_lba_range_blocks() wrapper.

Ah, I think I am understanding now. When the sector size is 4K the
minimum page sent with WRITE SAME will be 4K.

If so, we also need to fix the write_same SATL code that is working
under the assumption of a 512 byte sector sector as the largest
guaranteed amount of data in the associated sg pages.
Keying off of sector_size should be straight forward there...

-- 
Shaun Tancheff