On Wed, Jun 8, 2011 at 12:10 AM, FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx> wrote: > On Tue, 7 Jun 2011 23:56:21 -0700 > Dan Williams <dan.j.williams@xxxxxxxxx> wrote: > >> > The dma parameter restriction could be due to software (HBA drivers, >> > or subsystem). The value should be whatever the dma device driver says >> > it is in such case? >> >> I'm assuming that the dma driver is taking responsibility for setting >> this correctly. How would this work otherwise... HBA driver or >> subsystem queries the dmaengine device and then sets this parameter on >> its behalf? In other words dmanengine *is* the subsystem, if I am >> understanding your definition. > > Oops, I meant that the subsystem is software layer above > dmaengine. For example, SCSI subsystem sets the limit of max number of > sglist entries. That is, it is possible that software layer above > dmaengine could set dma limit, which is smaller than the limit of > dmaengine? > Perhaps, but this sounds like the reverse of what happens today where scsi device drivers with knowledge of their own hardware will tell the midlayer/subsystem the restriction. The change with regard to this patch is that the scsi device driver (for example) will recognize that the device it is driving will not be a bus master and will arrange to allocate a dma channel from dmaengine. When said scsi driver reports the dma restrictions to the subsystem it will borrow the parameters from the dma channel, not the scsi device. So yes, I still think it should be whatever the dma channel says. Although, you've been doing scsi work longer than I, so maybe I'm overlooking something...? Are there any cases today where the subsystem imposes tighter restrictions on the dma geometry than what the device reports? Even if that were the case it would be same situation that the scsi device driver reports maximum parameters, but the subsystem opts for something tighter. Whether the maximal parameters come from the scsi device or the dma channel is moot. -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
