From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stefan Richter Subject: Re: [PATCH 4/4] firewire: sbp2: remove overzealous alignment constraints Date: Fri, 18 May 2012 21:08:55 +0200 Message-ID: <20120518210855.43cc7e0b@stein> References: <4FB67AFC.7090402@ladisch.de> <4FB67BDD.2030707@ladisch.de> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4FB67BDD.2030707@ladisch.de> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linux1394-devel-bounces@lists.sourceforge.net To: Clemens Ladisch , linux-scsi@vger.kernel.org Cc: linux1394-devel@lists.sourceforge.net List-Id: linux-scsi@vger.kernel.org On May 18 Clemens Ladisch wrote at linux1394-devel: > The SBP-2/3 specifications do not require any alignment of data > buffers; only their own data structures need to be quadlet-aligned. SBP-2 clause 3.1.2.24 requires that system memory accepts quadlet r/w access. Memory which is not aligned at quadlet boundaries is not accessible by quadlet accesses per IEEE 1394 clause 6.2.5.2.2. > This patch is perfectly safe because there is no actual change: > the SCSI framework uses a default block queue DMA alignment of > 32 bits anyway. This code was added after recommendation to set it explicitly in the driver: http://marc.info/?l=linux-scsi&m=120137366708017 http://thread.gmane.org/gmane.linux.kernel.firewire.devel/11424 It is probably not going to happen that somebody decreases the SCSI default. But perhaps we should still keep this explicit...? > Signed-off-by: Clemens Ladisch > --- > drivers/firewire/sbp2.c | 8 ++------ > 1 files changed, 2 insertions(+), 6 deletions(-) > > --- a/drivers/firewire/sbp2.c > +++ b/drivers/firewire/sbp2.c > @@ -207,9 +207,8 @@ static const struct device *lu_dev(const struct sbp2_logical_unit *lu) > #define SBP2_MAX_CDB_SIZE 16 > > /* > - * The default maximum s/g segment size of a FireWire controller is > - * usually 0x10000, but SBP-2 only allows 0xffff. Since buffers have to > - * be quadlet-aligned, we set the length limit to 0xffff & ~3. > + * The maximum SBP-2 data buffer size is 0xffff. We quadlet-align this > + * for compatibility with earlier versions of this driver. > */ > #define SBP2_MAX_SEG_SIZE 0xfffc > > @@ -1530,9 +1529,6 @@ static int sbp2_scsi_slave_alloc(struct scsi_device *sdev) > > sdev->allow_restart = 1; > > - /* SBP-2 requires quadlet alignment of the data buffers. */ > - blk_queue_update_dma_alignment(sdev->request_queue, 4 - 1); > - > if (lu->tgt->workarounds & SBP2_WORKAROUND_INQUIRY_36) > sdev->inquiry_len = 36; > -- Stefan Richter -=====-===-- -=-= =--=- http://arcgraph.de/sr/ ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/