Date: Thu, 20 Sep 2012 22:23:07 +0300 From: Alexander Motin <mav@FreeBSD.org> To: jack sparrow <jacks.1785@gmail.com> Cc: freebsd-drivers@freebsd.org Subject: Re: Exclusive access of SCSI/ATA devices from user space Message-ID: <505B6D1B.7070506@FreeBSD.org> In-Reply-To: <5059CC56.8040705@FreeBSD.org> References: <CACmXQA09W56rSvVrprD8cuAbZ3T7hFmFKmfREiyXGOZwfpH5=g@mail.gmail.com> <201209190825.07384.jhb@freebsd.org> <5059CC56.8040705@FreeBSD.org>
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> Is there really no sorting of I/O requests inside cam passthrough > driver, or cam transport layer? Say if I send one i/o request to > selected device via cam passthrough driver and then send other one, > before previous one is completed. There is no sorting in pass driver, as it passes all requests to CAM immediately. CAM transport also does not intentionally sort requests during normal operation. In some rare error recovery cases it may be difficult to manage original request order during requests requeueing or retrying. CAM tries to do it right, but I am not sure it can be guarantied. > Do I need to modify cam transport layer also, to switch ata device > from PIO to DMA and vice versa for data transfer and to disable SATA > NCQ, and Command tag queing ; or CAM passthrough driver will be able > to do that. No, you don't need to modify. CAM provides APIs to control mode setting and command queuing via methods of the same PASS interface. If you are using pass interface, it is actually your duty to use proper command set (PIO/DMA/FPDMA) with the device, respecting current operation mode set by CAM. If CAM negotiated DMA with NCQ, you are free to use any of these kinds of commands in a mix you like. -- Alexander Motin
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