[PATCH 2/3] m68k/q40: add data_swab option for pata_falcon to byte-swap disk data

[Michael Schmitz <schmitzmic@gmail.com>]

Some users of pata_falcon on Q40 have IDE disks in default
IDE little endian byte order, whereas legacy disks use
host-native big-endian byte order as on the Atari Falcon.

Add module parameter 'data_swab' to allow connecting drives
with non-native data byte order. Drives selected by the
data_swap bit mask will have their user data byte-swapped to
host byte order, i.e. 'pata_falcon.data_swab=2' will byte-swap
all user data on drive B, leaving data on drive A in native
byte order. On Q40, drives on a second IDE interface may be
added to the bit mask as bits 2 and 3.

Default setting is no byte swapping, i.e. compatibility with
the native Falcon or Q40 operating system disk format.

Cc: William R Sowerbutts <will@sowerbutts.com>
Cc: Finn Thain <fthain@linux-m68k.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Michael Schmitz <schmitzmic@gmail.com>

---

Changes since RFC v4:

Geert Uytterhoeven:
- don't shift static module parameter for drive 3/4 bitmask
- simplify bit mask calculation to always use pdev->id

Finn Thain:
- correct bit numbers for drive 3/4

Changes since RFC v3:

- split off this byte swap handling into separate patch

- add hint regarding third and fourth drive on Q40

Finn Thain:
- rename module parameter to 'data_swab' to better reflect its use

William Sowerbutts:
- correct IDE drive number used in data swap conditional
---
 drivers/ata/pata_falcon.c | 26 +++++++++++++++++++++++++-
 1 file changed, 25 insertions(+), 1 deletion(-)

diff --git a/drivers/ata/pata_falcon.c b/drivers/ata/pata_falcon.c
index 346259e3bbc8..90488f565d6f 100644
--- a/drivers/ata/pata_falcon.c
+++ b/drivers/ata/pata_falcon.c
@@ -33,6 +33,16 @@
 #define DRV_NAME "pata_falcon"
 #define DRV_VERSION "0.1.0"
 
+static int pata_falcon_swap_mask;
+
+module_param_named(data_swab, pata_falcon_swap_mask, int, 0444);
+MODULE_PARM_DESC(data_swab, "Data byte swap enable/disable bitmap (0x1==drive1, 0x2==drive2, 0x4==drive3, 0x8==drive4, default==0)");
+
+struct pata_falcon_priv {
+	unsigned int swap_mask;
+	bool swap_data;
+};
+
 static const struct scsi_host_template pata_falcon_sht = {
 	ATA_PIO_SHT(DRV_NAME),
 };
@@ -44,13 +54,15 @@ static unsigned int pata_falcon_data_xfer(struct ata_queued_cmd *qc,
 	struct ata_device *dev = qc->dev;
 	struct ata_port *ap = dev->link->ap;
 	void __iomem *data_addr = ap->ioaddr.data_addr;
+	struct pata_falcon_priv *priv = ap->private_data;
 	unsigned int words = buflen >> 1;
 	struct scsi_cmnd *cmd = qc->scsicmd;
+	int dev_id = dev->devno;
 	bool swap = 1;
 
 	if (dev->class == ATA_DEV_ATA && cmd &&
 	    !blk_rq_is_passthrough(scsi_cmd_to_rq(cmd)))
-		swap = 0;
+		swap = priv->swap_data && (priv->swap_mask & BIT(dev_id));
 
 	/* Transfer multiple of 2 bytes */
 	if (rw == READ) {
@@ -123,6 +135,7 @@ static int __init pata_falcon_init_one(struct platform_device *pdev)
 	struct resource *base_res, *ctl_res, *irq_res;
 	struct ata_host *host;
 	struct ata_port *ap;
+	struct pata_falcon_priv *priv;
 	void __iomem *base, *ctl_base;
 	int irq = 0, io_offset = 1, reg_scale = 4;
 
@@ -165,6 +178,13 @@ static int __init pata_falcon_init_one(struct platform_device *pdev)
 	ap->pio_mask = ATA_PIO4;
 	ap->flags |= ATA_FLAG_SLAVE_POSS | ATA_FLAG_NO_IORDY;
 
+	priv = devm_kzalloc(&pdev->dev,
+		sizeof(struct pata_falcon_priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	ap->private_data = priv;
+
 	/* N.B. this assumes data_addr will be used for word-sized I/O only */
 	ap->ioaddr.data_addr = (void __iomem *)base_mem_res->start;
 
@@ -199,6 +219,10 @@ static int __init pata_falcon_init_one(struct platform_device *pdev)
 	ap->ioaddr.altstatus_addr	= ctl_base + io_offset;
 	ap->ioaddr.ctl_addr		= ctl_base + io_offset;
 
+	priv->swap_mask = pata_falcon_swap_mask >> (2 * pdev->id);
+	if (priv->swap_mask)
+		priv->swap_data = 1;
+
 	irq_res = platform_get_resource(pdev, IORESOURCE_IRQ, 0);
 	if (irq_res && irq_res->start > 0) {
 		irq = irq_res->start;
-- 
2.17.1