[PATCH v2 0/2] ata: DSM TRIM fix and improvements

[Niklas Cassel <cassel@kernel.org>]

Hello all,

This fixes DSM TRIM for 4Kn devices, which has ironically been broken
since commit ef2d7392c4ec ("libata: SCT Write Same / DSM Trim"), which
claimed to correct the DSM TRIM handling for 4Kn devices.


The first commit is a small fix that can be backported, which limits
the DSM TRIM to what we currently report in the Block Limits VPD page.
We currently report a single 512 byte page of entries, i.e. 64 Entries,
where each entry has a maximum of U16_MAX logical blocks.

The second commit:
-Improves the support by reading the MAX PAGES PER DSM COMMAND limit and
 populates the Block Limits VPD page accordingly.
-Modifies ata_scsi_write_same_xlat() to properly support up to this amount
 of pages.
-Removed the intermediate copying to ata_scsi_rbuf, writes to the scsi
 buffer directly.

Practically, sd still caps n_block at SD_MAX_WS16_BLOCKS
(~3 pages actually used on 4Kn), so while removing the limit on
ATA_SCSI_RBUF_SIZE (2048) - i.e. 4 pages), we will still be limited
by SD_MAX_WS16_BLOCKS. The main improvement is not longer taking the
ata_scsi_rbuf_lock and doing and extra copy from ata_scsi_rbuf.


Changes since v1:
-Picked up tags from Hannes.
-Cast to u64 to avoid potential overflow when using 32-bit arithmetic.
-If no limit is reported, assume that only a single 512-byte page is
 supported.


Niklas Cassel (2):
  ata: libata-scsi: fix DSM TRIM for sector sizes larger than 2048 bytes
  ata: libata-scsi: scale DSM TRIM payload by MAX PAGES PER DSM COMMAND

 drivers/ata/libata-scsi.c | 137 ++++++++++++++++++++++++++------------
 include/linux/ata.h       |  13 ++++
 2 files changed, 108 insertions(+), 42 deletions(-)

-- 
2.55.0