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<!-- received="Fri Dec 17 05:57:28 1999 PST" -->
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<!-- sent="Fri, 17 Dec 1999 08:57:15 -0500" -->
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<!-- name="Douglas Gilbert" -->
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<!-- email="dgilbert@interlog.com" -->
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<!-- subject="Re: Linux sg and sense codes" -->
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<!-- inreplyto="Linux sg and sense codes" -->
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<title>sane-devel: Re: Linux sg and sense codes</title>
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<h1>Re: Linux sg and sense codes</h1>
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<b>Douglas Gilbert</b> (<a href="mailto:dgilbert@interlog.com"><i>dgilbert@interlog.com</i></a>)<br>
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<i>Fri, 17 Dec 1999 08:57:15 -0500</i>
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<p>
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<ul>
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<li> <b>Messages sorted by:</b> <a href="date.html#115">[ date ]</a><a href="index.html#115">[ thread ]</a><a href="subject.html#115">[ subject ]</a><a href="author.html#115">[ author ]</a>
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<li> <b>Next message:</b> <a href="0116.html">Matto Marjanovic: "Re: Linux sg and sense codes"</a>
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<li> <b>Previous message:</b> <a href="0114.html">Christian: "Re: SN: What is SANE ?"</a>
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<li> <b>Maybe in reply to:</b> <a href="0112.html">Matto Marjanovic: "Linux sg and sense codes"</a>
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<!-- nextthread="start" -->
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<li> <b>Next in thread:</b> <a href="0116.html">Matto Marjanovic: "Re: Linux sg and sense codes"</a>
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</ul>
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<!-- body="start" -->
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Matto Marjanovic wrote:<br>
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<i>> </i><br>
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<i>> Hiya, given all the new development in the Linux scsi architecture, I</i><br>
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<i>> figured I'd ask about an old thorn in my side (which seems to have</i><br>
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<i>> started poking me again recently).</i><br>
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<i>> </i><br>
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<i>> Older Microtek scanners, despite setting the "valid" bit of the first</i><br>
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<i>> byte of the sense buffer, return sense codes which bear no relation</i><br>
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<i>> to the SCSI-2 standard. A couple of years ago I figured out that</i><br>
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<i>> this tended to really confuse the scsi system, which would sometimes</i><br>
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<i>> retry commands on its own, and would inevitably *not* return the</i><br>
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<i>> sense data to the backend without munging it up in some way.</i><br>
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<i>> </i><br>
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<i>> This is a real nuisance because some scanners try and need to report</i><br>
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<i>> that they are busy in certain circumstances, but the message is</i><br>
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<i>> always lost. The fact that the scsi system retries the commands on</i><br>
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<i>> its own volition just compounds the problem.</i><br>
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<i>> </i><br>
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<i>> Do you know if anything has changed in this regard, or if there are</i><br>
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<i>> any ways to circumvent this snag?</i><br>
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<p>
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Garbage in, surprises out. Have things changed? Well as<br>
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I found out recently this is a relatively complex question<br>
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in the case of the linux scsi sub-system. The answer <br>
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depends on which of the 2 error processing regimes <br>
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available that your adapter driver uses.<br>
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<p>
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If the newer regime is used ("eh_code") then the request<br>
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by the sg driver for no retries is almost always honoured.<br>
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So there shouldn't be any retries, resets, etc<br>
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<p>
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If the older regime is used then the situation described<br>
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above occurs. [If the ".h" or the ".c" file of your<br>
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adapter source contains something like:<br>
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use_new_eh_code: 1<br>
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then this is the newer regime. If not, it is using the older<br>
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regime.]<br>
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<p>
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Unfortunately, a large majority of linux scsi adapter drivers<br>
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(including aic7xxx) use the older regime. The maintainer of<br>
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the scsi mid level, Eric Youngdale, has renewed his push<br>
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for the adapter driver maintainers to upgrade to the newer<br>
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regime. The nature of open software development makes it<br>
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difficult to force such an issue too hard but things are<br>
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changing slowly.<br>
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<p>
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Sorry the answer couldn't be a bit more positive.<br>
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<p>
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<p>
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On a brighter note, the 2.3 linux kernel developmemt tree<br>
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contains a usb_scsi pseudo adapter driver. This opens<br>
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up the possibility of using SANE on USB scanners that<br>
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uses a scsi command set. Does anyone know of USB scanner<br>
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models that use a scsi command set? [Oliver Rauch told me<br>
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yesterday that he thinks the Umax 2200 falls into this<br>
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group.]<br>
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<p>
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Doug Gilbert<br>
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<p>
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<pre>
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--
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</pre>
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<!-- body="end" -->
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<p>
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<ul>
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<!-- next="start" -->
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<li> <b>Next message:</b> <a href="0116.html">Matto Marjanovic: "Re: Linux sg and sense codes"</a>
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<li> <b>Previous message:</b> <a href="0114.html">Christian: "Re: SN: What is SANE ?"</a>
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<li> <b>Maybe in reply to:</b> <a href="0112.html">Matto Marjanovic: "Linux sg and sense codes"</a>
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<!-- nextthread="start" -->
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<li> <b>Next in thread:</b> <a href="0116.html">Matto Marjanovic: "Re: Linux sg and sense codes"</a>
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<!-- reply="end" -->
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</ul>
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