From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Martin Peschke3" Subject: Re: ide-scsi data transfer residuals Date: Mon, 8 Jul 2002 18:17:26 +0200 Sender: linux-ide-owner@vger.kernel.org Message-ID: Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: List-Id: linux-ide@vger.kernel.org To: Douglas Gilbert Cc: tonyb@cybernetics.com, linux-scsi@vger.kernel.org, linux-ide@vger.kernel.org Hi, unfortunately the residual count is not used by high level SCSI drivers like sd and sr to recover partial data transfers, as far as I can see. That's dangerous. Mit freundlichen Gr=FC=DFen / with kind regards Martin Peschke IBM Deutschland Entwicklung GmbH Linux for eServer Development Phone: +49-(0)7031-16-2349 Douglas Gilbert @vger.kernel.org on 07/06/2002 04:10:= 01 AM Please respond to Douglas Gilbert Sent by: linux-scsi-owner@vger.kernel.org To: tonyb@cybernetics.com cc: linux-scsi@vger.kernel.org, linux-ide@vger.kernel.org Subject: Re: ide-scsi data transfer residuals Tony Battersby wrote: > > Hello, > > I am using the scsi-generic and ide-scsi drivers together for low-lev= el > access to an IDE tape drive (vanilla 2.4.17). I noticed that the dat= a > transfer residual in sg_io_hdr_t { int resid; } is always zero. I as= sume > that the residual calculation is just a missing feature from the ide-= scsi > driver. Does anyone know how hard it is to add it? Tony, Support for the residual count is optional. A inaccurate survey shows these adapter drivers support it: advansys aha152x aic7xxx_old (but not the newer aic7xxx) dc395x_trm scsiiom sym53c8xx sym53c8xx_2 I do not know how the ide-scsi driver would get the information. However here is the calculation it should do: Scsi_Cmnd::resid =3D Scsi_Cmnd::bufflen - Of the drivers that support "resid" most given a scatter gather list will use the sum of the element lengths instead of bufflen. Unfortunately that sum can be larger the bufflen due to padding and alignment requirements of the most backward DMA engines out there (I was burnt by the aha1542 ISA card). IOW HBA driver writers, please use bufflen. Perhaps the CAM name of "dxfer_len" would be clearer for this field. Doug Gilbert - To unsubscribe from this list: send the line "unsubscribe linux-scsi" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html