Never mind. I misread. I thought q->limits.max_sectors = min(rw_max, queue_max_hw_sectors(q)); can be run when rw_max is not set. On 4 June 2016 at 23:18, Long Li <longli@xxxxxxxxxxxxx> wrote: > Sorry, "redundant check" is not the best word to describe this patch. > > The result of this patch is that: > 1. if opt_xfer_blocks has a valid value (returned form VPD BLOCK LIMITS), use it to set max_sectors > 2. if opt_xfer_blocks doesn't have a valid value, leave max_sectors unchanged > > The reason is that, max_sectors already has value at this point, the default value is SCSI_DEFAULT_MAX_SECTORS (include/scsi/scsi_host.h). The lower layer host driver can change this value in its template. I think the drivers care about this value have already set it. So it's better not to change it again. If they want max_sectors to be set by sd, they can use BLOCK LIMITS VPD to tell it to do so. > > >> -----Original Message----- >> From: Tom Yan [mailto:tom.ty89@xxxxxxxxx] >> Sent: Saturday, June 4, 2016 1:41 AM >> To: Long Li <longli@xxxxxxxxxxxxx> >> Cc: James E.J. Bottomley <jejb@xxxxxxxxxxxxxxxxxx>; Martin K. Petersen >> <martin.petersen@xxxxxxxxxx>; linux-scsi@xxxxxxxxxxxxxxx; linux- >> kernel@xxxxxxxxxxxxxxx >> Subject: Re: [PATCH] sd: remove redundant check for >> BLK_DEF_MAX_SECTORS >> >> The main point there is not to check q->limits.max_sectors against >> BLK_DEF_MAX_SECTORS, but sdkp->opt_xfer_blocks against >> SD_DEF_XFER_BLOCKS et al.? `rw_max = BLK_DEF_MAX_SECTORS;` there is >> merely the fallback when sdkp->opt_xfer_blocks does not pass the >> conditions. With your patch `rw_max` can be indeterminate in those >> circumstances. >> >> On 4 June 2016 at 11:57, Long Li <longli@xxxxxxxxxxxxx> wrote: >> > q->limits.max_sectors is already checked against BLK_DEF_MAX_SECTORS >> in __scsi_alloc_queue(), when it calls blk_queue_max_hw_sectors(). There >> is no need to check it again in sd. >> > >> > This change also allows a SCSI driver set an maximum sector size bigger >> than BLK_DEF_MAX_SECTORS, without returning values on optional VPD >> page 0xb0 "Block Limits". >> > >> > Signed-off-by: Long Li <longli@xxxxxxxxxxxxx> >> > >> > --- >> > drivers/scsi/sd.c | 7 ++----- >> > 1 file changed, 2 insertions(+), 5 deletions(-) >> > >> > diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c index >> > 60bff78..d8c4047 100644 >> > --- a/drivers/scsi/sd.c >> > +++ b/drivers/scsi/sd.c >> > @@ -2870,11 +2870,8 @@ static int sd_revalidate_disk(struct gendisk *disk) >> > logical_to_bytes(sdp, sdkp->opt_xfer_blocks) >= PAGE_SIZE) { >> > q->limits.io_opt = logical_to_bytes(sdp, sdkp->opt_xfer_blocks); >> > rw_max = logical_to_sectors(sdp, sdkp->opt_xfer_blocks); >> > - } else >> > - rw_max = BLK_DEF_MAX_SECTORS; >> > - >> > - /* Combine with controller limits */ >> > - q->limits.max_sectors = min(rw_max, queue_max_hw_sectors(q)); >> > + q->limits.max_sectors = min(rw_max, >> queue_max_hw_sectors(q)); >> > + } >> > >> > set_capacity(disk, logical_to_sectors(sdp, sdkp->capacity)); >> > sd_config_write_same(sdkp); >> > -- >> > 2.7.4 >> > >> > -- >> > To unsubscribe from this list: send the line "unsubscribe linux-scsi" >> > in the body of a message to majordomo@xxxxxxxxxxxxxxx More >> majordomo >> > info at >> > https://na01.safelinks.protection.outlook.com/?url=http%3a%2f%2fvger.k >> > ernel.org%2fmajordomo- >> info.html&data=01%7c01%7clongli%40microsoft.com% >> > >> 7ce142128958ec47629dbe08d38c540306%7c72f988bf86f141af91ab2d7cd011d >> b47% >> > 7c1&sdata=EjjF86cvJqaxOAOWnN0%2f3Qln05qcquwe%2fKA7DgEjtcI%3d -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
