I just spent a bunch of time digging through the ATA driver to figure out why
OpenSolaris as a QEMU guest wouldn't work without setting
atapi-cd-dma-enabled=0 from GRUB.
This code doesn't disable DMA because for ATAPI (the simulated device is ATA-4)
it says the capability bit is defunct.
2184 /*
2185 * DMA mode is mandatory on ATA-3 (or newer) drives but is
2186 * optional on ATA-2 (or older) drives.
2187 *
2188 * On ATA-2 drives the ai_majorversion word will probably
2189 * be 0xffff or 0x0000, check the (now obsolete) DMA bit in
2190 * the capabilities word instead. The order of these tests
2191 * is important since an ATA-3 drive doesn't have to set
2192 * the DMA bit in the capabilities word.
2193 *
2194 */
2195
2196 if (!((ata_drvp->ad_id.ai_majorversion & 0x8000) == 0 &&
2197 ata_drvp->ad_id.ai_majorversion >= (1 << 2)) &&
2198 !(ata_drvp->ad_id.ai_cap & ATAC_DMA_SUPPORT)) {
2199 ata_dev_DMA_sel_msg = "device not DMA capable";
2200
2201 return (ATA_DMA_OFF);
2202 }
Does anyone have any suggestions on how best to handle this? Should I just add
another entry to the blacklist? Or, is there a better way of detecting if an
ATAPI device is really DMA capable and falling back to PIO if it isn't?
- Eric
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