+ /* we must lengthen transfers to end on a 32-bit boundary */
+ qc->pad_len = lsg->length & 3;
+ if (qc->pad_len) {
+ void *pad_buf = ap->pad + (qc->tag * ATA_DMA_PAD_SZ);
+ struct scatterlist *psg = &qc->pad_sgent;
+ unsigned int offset;
+
+ assert(qc->dev->class == ATA_DEV_ATAPI);
+
+ memset(pad_buf, 0, ATA_DMA_PAD_SZ);
+
+ /*
+ * psg->page/offset are used to copy to-be-written
+ * data in this function or read data in ata_sg_clean.
+ */
+ offset = lsg->offset + lsg->length - qc->pad_len;
+ psg->page = nth_page(lsg->page, offset >> PAGE_SHIFT);
+ psg->offset = offset_in_page(offset);
+
+ if (qc->tf.flags & ATA_TFLAG_WRITE) {
+ void *addr = kmap_atomic(psg->page, KM_IRQ0);
+ memcpy(pad_buf, addr + psg->offset, qc->pad_len);
+ kunmap_atomic(psg->page, KM_IRQ0);
+ }
+
+ sg_dma_address(psg) = ap->pad_dma + (qc->tag * ATA_DMA_PAD_SZ);
+ sg_dma_len(psg) = ATA_DMA_PAD_SZ;
+ /* trim last sg */
+ lsg->length -= qc->pad_len;
+
+ DPRINTK("padding done, sg[%d].length=%u pad_len=%u\n",
+ qc->n_elem - 1, lsg->length, qc->pad_len);
+ }
+