Re: [PATCH RFC v3 2/2] m68k/q40: add data_swab option for pata_falcon to byte-swap disk data

Finn Thain
2023-08-17T10:17:08Z

On Thu, 17 Aug 2023, Michael Schmitz wrote:

> Some users of pata_falcon on Q40 have IDE disks in classic
> little endian byte order, whereas legacy disks use 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 3 and 4.

Many would say that's off by one, as it's popular to number the LSB as bit
zero.

>
> 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 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 | 29 ++++++++++++++++++++++++++++-
> 1 file changed, 28 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/ata/pata_falcon.c b/drivers/ata/pata_falcon.c
> index 346259e3bbc8..cec3c3a6eed9 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;
>
> @@ -165,10 +178,20 @@ 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;
>
> if (base_res) { /* only Q40 has IO resources */
> + if (pdev->id)
> + pata_falcon_swap_mask >>= 2;
> + priv->swap_mask = pata_falcon_swap_mask;
> io_offset = 0x10000;
> reg_scale = 1;
> base = (void __iomem *)base_res->start;
> @@ -178,6 +201,7 @@ static int __init pata_falcon_init_one(struct platform_device *pdev)
> &base_res->start,
> &ctl_res->start);
> } else {
> + priv->swap_mask = pata_falcon_swap_mask;
> base = (void __iomem *)base_mem_res->start;
> ctl_base = (void __iomem *)ctl_mem_res->start;
>
> @@ -199,6 +223,9 @@ 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;
>
> + 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;
>

I think the patch could be simplified by dropping the dynamic memory
allocation...

diff --git a/drivers/ata/pata_falcon.c b/drivers/ata/pata_falcon.c
index 346259e3bbc8..d057f11ec02d 100644
--- a/drivers/ata/pata_falcon.c
+++ b/drivers/ata/pata_falcon.c
@@ -33,6 +33,11 @@
#define DRV_NAME "pata_falcon"
#define DRV_VERSION "0.1.0"

+static int pata_falcon_data_swab;
+
+module_param_named(data_swab, pata_falcon_data_swab, int, 0444);
+MODULE_PARM_DESC(data_swab, "Data byte swap enable/disable bitmap (0x1==drive1, 0x2==drive2, 0x4==drive3, 0x8==drive4, default: 0)");
+
static const struct scsi_host_template pata_falcon_sht = {
ATA_PIO_SHT(DRV_NAME),
};
@@ -50,7 +55,7 @@ static unsigned int pata_falcon_data_xfer(struct ata_queued_cmd *qc,

if (dev->class == ATA_DEV_ATA && cmd &&
!blk_rq_is_passthrough(scsi_cmd_to_rq(cmd)))
- swap = 0;
+ swap = (int)ap->private_data & BIT(dev->devno);

/* Transfer multiple of 2 bytes */
if (rw == READ) {
@@ -199,6 +204,8 @@ 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;

+ ap->private_data = (void *)((pata_falcon_data_swab >> (2 * pdev->id)) & 3);
+
irq_res = platform_get_resource(pdev, IORESOURCE_IRQ, 0);
if (irq_res && irq_res->start > 0) {
irq = irq_res->start;