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SubjectRe: [PATCH v5 2/2] Add support for SCT Write Same
I don't really know about SCT Write Same but there is one concern I
could I think of.

libata's SATL would report a maximum write same length base on the
number of sectors a one-block TRIM payload can describe at most, which
is 65535 * 64 = 4194240 (see ata_scsiop_inq_b0 in libata-scsi.c). If
the drive does not support TRIM, it will not report such length. That
is technically fine, as per SBC standard, and I suppose the SCSI disk
driver would use SD_MAX_WS16_BLOCKS = 0x7fffff (8388607).

However, are both of the limits fine for SCT Write Same? Any alignment
concern? Also, is such "inconsistency" acceptable?

On 10 August 2016 at 01:00, Shaun Tancheff <shaun@tancheff.com> wrote:
> SATA drives may support write same via SCT. This is useful
> for setting the drive contents to a specific pattern (0's).
>
> Translate a SCSI WRITE SAME command to be either a DSM TRIM command or
> an SCT Write Same command.
>
> Based on the UNMAP flag:
> - When set translate to DSM TRIM
> - When not set translate to SCT Write Same
>
> Signed-off-by: Shaun Tancheff <shaun.tancheff@seagate.com>
> ---
> v5:
> - Addressed review comments
> - Report support for ZBC only for zoned devices.
> - kmap page during rewrite
> - Fix unmap set to require trim or error, if not unmap then sct write
> same or error.
> v4:
> - Added partial MAINTENANCE_IN opcode simulation
> - Dropped all changes in drivers/scsi/*
> - Changed to honor the UNMAP flag -> TRIM, no UNMAP -> SCT.
> v3:
> - Demux UNMAP/TRIM from WRITE SAME
> v2:
> - Remove fugly ata hacking from sd.c
> ---
> drivers/ata/libata-scsi.c | 189 +++++++++++++++++++++++++++++++++++++++-------
> include/linux/ata.h | 43 +++++++++++
> 2 files changed, 205 insertions(+), 27 deletions(-)
>
> diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
> index a71067a..99b0e6c 100644
> --- a/drivers/ata/libata-scsi.c
> +++ b/drivers/ata/libata-scsi.c
> @@ -1159,8 +1159,6 @@ static void ata_scsi_sdev_config(struct scsi_device *sdev)
> {
> sdev->use_10_for_rw = 1;
> sdev->use_10_for_ms = 1;
> - sdev->no_report_opcodes = 1;
> - sdev->no_write_same = 1;
>
> /* Schedule policy is determined by ->qc_defer() callback and
> * it needs to see every deferred qc. Set dev_blocked to 1 to
> @@ -3325,6 +3323,41 @@ static unsigned int ata_format_dsm_trim_descr(struct scatterlist *sg, u32 num,
> return used_bytes;
> }
>
> +/**
> + * ata_format_dsm_trim_descr() - SATL Write Same to ATA SCT Write Same
> + * @sg: Scatter / Gather list attached to command.
> + * @lba: Starting sector
> + * @num: Number of bytes to be zero'd.
> + *
> + * Rewrite the WRITE SAME descriptor to be an SCT Write Same formatted
> + * descriptor.
> + * NOTE: Writes a pattern (0's) in the foreground.
> + * Large write-same requents can timeout.
> + */
> +static void ata_format_sct_write_same(struct scatterlist *sg, u64 lba, u64 num)
> +{
> + void *ptr = kmap_atomic(sg_page(sg));
> + u16 *sctpg = ptr + sg->offset;
> +
> + put_unaligned_le16(0x0002, &sctpg[0]); /* SCT_ACT_WRITE_SAME */
> + put_unaligned_le16(0x0101, &sctpg[1]); /* WRITE PTRN FG */
> + put_unaligned_le64(lba, &sctpg[2]);
> + put_unaligned_le64(num, &sctpg[6]);
> + put_unaligned_le32(0u, &sctpg[10]);
> +
> + kunmap_atomic(ptr);
> +}
> +
> +/**
> + * ata_scsi_write_same_xlat() - SATL Write Same to ATA SCT Write Same
> + * @qc: Command to be translated
> + *
> + * Translate a SCSI WRITE SAME command to be either a DSM TRIM command or
> + * an SCT Write Same command.
> + * Based on WRITE SAME has the UNMAP flag
> + * When set translate to DSM TRIM
> + * When clear translate to SCT Write Same
> + */
> static unsigned int ata_scsi_write_same_xlat(struct ata_queued_cmd *qc)
> {
> struct ata_taskfile *tf = &qc->tf;
> @@ -3338,6 +3371,7 @@ static unsigned int ata_scsi_write_same_xlat(struct ata_queued_cmd *qc)
> u32 size;
> u16 fp;
> u8 bp = 0xff;
> + u8 unmap = cdb[1] & 0x8;
>
> /* we may not issue DMA commands if no DMA mode is set */
> if (unlikely(!dev->dma_mode))
> @@ -3350,10 +3384,23 @@ static unsigned int ata_scsi_write_same_xlat(struct ata_queued_cmd *qc)
> scsi_16_lba_len(cdb, &block, &n_block);
>
> /* for now we only support WRITE SAME with the unmap bit set */
> - if (unlikely(!(cdb[1] & 0x8))) {
> - fp = 1;
> - bp = 3;
> - goto invalid_fld;
> + if (unmap) {
> + if ((dev->horkage & ATA_HORKAGE_NOTRIM) ||
> + !ata_id_has_trim(dev->id)) {
> + fp = 1;
> + bp = 3;
> + goto invalid_fld;
> + }
> + if (n_block > 0xffff * trmax) {
> + fp = 2;
> + goto invalid_fld;
> + }
> + } else {
> + if (!ata_id_sct_write_same(dev->id)) {
> + fp = 1;
> + bp = 3;
> + goto invalid_fld;
> + }
> }
>
> /*
> @@ -3364,30 +3411,42 @@ static unsigned int ata_scsi_write_same_xlat(struct ata_queued_cmd *qc)
> goto invalid_param_len;
>
> sg = scsi_sglist(scmd);
> - if (n_block <= 0xffff * cmax) {
> + if (unmap) {
> size = ata_format_dsm_trim_descr(sg, trmax, block, n_block);
> + if (ata_ncq_enabled(dev) && ata_fpdma_dsm_supported(dev)) {
> + /* Newer devices support queued TRIM commands */
> + tf->protocol = ATA_PROT_NCQ;
> + tf->command = ATA_CMD_FPDMA_SEND;
> + tf->hob_nsect = ATA_SUBCMD_FPDMA_SEND_DSM & 0x1f;
> + tf->nsect = qc->tag << 3;
> + tf->hob_feature = (size / 512) >> 8;
> + tf->feature = size / 512;
> +
> + tf->auxiliary = 1;
> + } else {
> + tf->protocol = ATA_PROT_DMA;
> + tf->hob_feature = 0;
> + tf->feature = ATA_DSM_TRIM;
> + tf->hob_nsect = (size / 512) >> 8;
> + tf->nsect = size / 512;
> + tf->command = ATA_CMD_DSM;
> + }
> } else {
> - fp = 2;
> - goto invalid_fld;
> - }
> -
> - if (ata_ncq_enabled(dev) && ata_fpdma_dsm_supported(dev)) {
> - /* Newer devices support queued TRIM commands */
> - tf->protocol = ATA_PROT_NCQ;
> - tf->command = ATA_CMD_FPDMA_SEND;
> - tf->hob_nsect = ATA_SUBCMD_FPDMA_SEND_DSM & 0x1f;
> - tf->nsect = qc->tag << 3;
> - tf->hob_feature = (size / 512) >> 8;
> - tf->feature = size / 512;
> + ata_format_sct_write_same(sg, block, n_block);
>
> - tf->auxiliary = 1;
> - } else {
> - tf->protocol = ATA_PROT_DMA;
> tf->hob_feature = 0;
> - tf->feature = ATA_DSM_TRIM;
> - tf->hob_nsect = (size / 512) >> 8;
> - tf->nsect = size / 512;
> - tf->command = ATA_CMD_DSM;
> + tf->feature = 0;
> + tf->hob_nsect = 0;
> + tf->nsect = 1;
> + tf->lbah = 0;
> + tf->lbam = 0;
> + tf->lbal = ATA_CMD_STANDBYNOW1;
> + tf->hob_lbah = 0;
> + tf->hob_lbam = 0;
> + tf->hob_lbal = 0;
> + tf->device = ATA_CMD_STANDBYNOW1;
> + tf->protocol = ATA_PROT_DMA;
> + tf->command = ATA_CMD_WRITE_LOG_DMA_EXT;
> }
>
> tf->flags |= ATA_TFLAG_ISADDR | ATA_TFLAG_DEVICE | ATA_TFLAG_LBA48 |
> @@ -3411,6 +3470,76 @@ invalid_opcode:
> }
>
> /**
> + * ata_scsiop_maint_in - Simulate a subset of MAINTENANCE_IN
> + * @args: device MAINTENANCE_IN data / SCSI command of interest.
> + * @rbuf: Response buffer, to which simulated SCSI cmd output is sent.
> + *
> + * Yields a subset to satisfy scsi_report_opcode()
> + *
> + * LOCKING:
> + * spin_lock_irqsave(host lock)
> + */
> +static unsigned int ata_scsiop_maint_in(struct ata_scsi_args *args, u8 *rbuf)
> +{
> + struct ata_device *dev = args->dev;
> + u8 *cdb = args->cmd->cmnd;
> + u8 supported = 0;
> + unsigned int err = 0;
> +
> + if (cdb[2] != 1) {
> + ata_dev_warn(dev, "invalid command format %d\n", cdb[2]);
> + err = 2;
> + goto out;
> + }
> + switch (cdb[3]) {
> + case INQUIRY:
> + case MODE_SENSE:
> + case MODE_SENSE_10:
> + case READ_CAPACITY:
> + case SERVICE_ACTION_IN_16:
> + case REPORT_LUNS:
> + case REQUEST_SENSE:
> + case SYNCHRONIZE_CACHE:
> + case REZERO_UNIT:
> + case SEEK_6:
> + case SEEK_10:
> + case TEST_UNIT_READY:
> + case SEND_DIAGNOSTIC:
> + case MAINTENANCE_IN:
> + case READ_6:
> + case READ_10:
> + case READ_16:
> + case WRITE_6:
> + case WRITE_10:
> + case WRITE_16:
> + case ATA_12:
> + case ATA_16:
> + case VERIFY:
> + case VERIFY_16:
> + case MODE_SELECT:
> + case MODE_SELECT_10:
> + case START_STOP:
> + supported = 3;
> + break;
> + case WRITE_SAME_16:
> + if (ata_id_sct_write_same(dev->id))
> + supported = 3;
> + break;
> + case ZBC_IN:
> + case ZBC_OUT:
> + if (ata_id_zoned_cap(dev->id) ||
> + dev->class == ATA_DEV_ZAC)
> + supported = 3;
> + break;
> + default:
> + break;
> + }
> +out:
> + rbuf[1] = supported; /* supported */
> + return err;
> +}
> +
> +/**
> * ata_scsi_report_zones_complete - convert ATA output
> * @qc: command structure returning the data
> *
> @@ -4190,6 +4319,13 @@ void ata_scsi_simulate(struct ata_device *dev, struct scsi_cmnd *cmd)
> ata_scsi_invalid_field(dev, cmd, 1);
> break;
>
> + case MAINTENANCE_IN:
> + if (scsicmd[1] == MI_REPORT_SUPPORTED_OPERATION_CODES)
> + ata_scsi_rbuf_fill(&args, ata_scsiop_maint_in);
> + else
> + ata_scsi_invalid_field(dev, cmd, 1);
> + break;
> +
> /* all other commands */
> default:
> ata_scsi_set_sense(dev, cmd, ILLEGAL_REQUEST, 0x20, 0x0);
> @@ -4222,7 +4358,6 @@ int ata_scsi_add_hosts(struct ata_host *host, struct scsi_host_template *sht)
> shost->max_lun = 1;
> shost->max_channel = 1;
> shost->max_cmd_len = 16;
> - shost->no_write_same = 1;
>
> /* Schedule policy is determined by ->qc_defer()
> * callback and it needs to see every deferred qc.
> diff --git a/include/linux/ata.h b/include/linux/ata.h
> index 45a1d71..fdb1803 100644
> --- a/include/linux/ata.h
> +++ b/include/linux/ata.h
> @@ -105,6 +105,7 @@ enum {
> ATA_ID_CFA_KEY_MGMT = 162,
> ATA_ID_CFA_MODES = 163,
> ATA_ID_DATA_SET_MGMT = 169,
> + ATA_ID_SCT_CMD_XPORT = 206,
> ATA_ID_ROT_SPEED = 217,
> ATA_ID_PIO4 = (1 << 1),
>
> @@ -789,6 +790,48 @@ static inline bool ata_id_sense_reporting_enabled(const u16 *id)
> }
>
> /**
> + *
> + * Word: 206 - SCT Command Transport
> + * 15:12 - Vendor Specific
> + * 11:6 - Reserved
> + * 5 - SCT Command Transport Data Tables supported
> + * 4 - SCT Command Transport Features Control supported
> + * 3 - SCT Command Transport Error Recovery Control supported
> + * 2 - SCT Command Transport Write Same supported
> + * 1 - SCT Command Transport Long Sector Access supported
> + * 0 - SCT Command Transport supported
> + */
> +static inline bool ata_id_sct_data_tables(const u16 *id)
> +{
> + return id[ATA_ID_SCT_CMD_XPORT] & (1 << 5) ? true : false;
> +}
> +
> +static inline bool ata_id_sct_features_ctrl(const u16 *id)
> +{
> + return id[ATA_ID_SCT_CMD_XPORT] & (1 << 4) ? true : false;
> +}
> +
> +static inline bool ata_id_sct_error_recovery_ctrl(const u16 *id)
> +{
> + return id[ATA_ID_SCT_CMD_XPORT] & (1 << 3) ? true : false;
> +}
> +
> +static inline bool ata_id_sct_write_same(const u16 *id)
> +{
> + return id[ATA_ID_SCT_CMD_XPORT] & (1 << 2) ? true : false;
> +}
> +
> +static inline bool ata_id_sct_long_sector_access(const u16 *id)
> +{
> + return id[ATA_ID_SCT_CMD_XPORT] & (1 << 1) ? true : false;
> +}
> +
> +static inline bool ata_id_sct_supported(const u16 *id)
> +{
> + return id[ATA_ID_SCT_CMD_XPORT] & (1 << 0) ? true : false;
> +}
> +
> +/**
> * ata_id_major_version - get ATA level of drive
> * @id: Identify data
> *
> --
> 2.8.1
>
> --
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