swim3: support highmem

swim3 only uses the virtual address of a bio to stash it into the data
transfer using virt_to_bus. But the ppc32 virt_to_bus just uses the
physical address with an offset. Replace virt_to_bus with a local hack
that performs the equivalent transformation and stop asking for block
layer bounce buffering.

Signed-off-by: Christoph Hellwig <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jens Axboe <[e-mail]>

drivers/block/swim3.c

···
 };
 
 static void seek_track(struct floppy_state *fs, int n);
-static void init_dma(struct dbdma_cmd *cp, int cmd, void *buf, int count);
 static void act(struct floppy_state *fs);
 static void scan_timeout(struct timer_list *t);
 static void seek_timeout(struct timer_list *t);
···
 	fs->settle_time = 0;
 }
 
+/*
+ * XXX: this is a horrible hack, but at least allows ppc32 to get
+ * out of defining virt_to_bus, and this driver out of using the
+ * deprecated block layer bounce buffering for highmem addresses
+ * for no good reason.
+ */
+static unsigned long swim3_phys_to_bus(phys_addr_t paddr)
+{
+	return paddr + PCI_DRAM_OFFSET;
+}
+
+static phys_addr_t swim3_bio_phys(struct bio *bio)
+{
+	return page_to_phys(bio_page(bio)) + bio_offset(bio);
+}
+
 static inline void init_dma(struct dbdma_cmd *cp, int cmd,
-			    void *buf, int count)
+			    phys_addr_t paddr, int count)
 {
 	cp->req_count = cpu_to_le16(count);
 	cp->command = cpu_to_le16(cmd);
-	cp->phy_addr = cpu_to_le32(virt_to_bus(buf));
+	cp->phy_addr = cpu_to_le32(swim3_phys_to_bus(paddr));
 	cp->xfer_status = 0;
 }
 
···
 	out_8(&sw->sector, fs->req_sector);
 	out_8(&sw->nsect, n);
 	out_8(&sw->gap3, 0);
-	out_le32(&dr->cmdptr, virt_to_bus(cp));
+	out_le32(&dr->cmdptr, swim3_phys_to_bus(virt_to_phys(cp)));
 	if (rq_data_dir(req) == WRITE) {
 		/* Set up 3 dma commands: write preamble, data, postamble */
-		init_dma(cp, OUTPUT_MORE, write_preamble, sizeof(write_preamble));
+		init_dma(cp, OUTPUT_MORE, virt_to_phys(write_preamble),
+			 sizeof(write_preamble));
 		++cp;
-		init_dma(cp, OUTPUT_MORE, bio_data(req->bio), 512);
+		init_dma(cp, OUTPUT_MORE, swim3_bio_phys(req->bio), 512);
 		++cp;
-		init_dma(cp, OUTPUT_LAST, write_postamble, sizeof(write_postamble));
+		init_dma(cp, OUTPUT_LAST, virt_to_phys(write_postamble),
+			sizeof(write_postamble));
 	} else {
-		init_dma(cp, INPUT_LAST, bio_data(req->bio), n * 512);
+		init_dma(cp, INPUT_LAST, swim3_bio_phys(req->bio), n * 512);
 	}
 	++cp;
 	out_le16(&cp->command, DBDMA_STOP);
···
 		disk->queue = NULL;
 		goto out_put_disk;
 	}
-	blk_queue_bounce_limit(disk->queue, BLK_BOUNCE_HIGH);
 	disk->queue->queuedata = fs;
 
 	rc = swim3_add_device(mdev, floppy_count);