Re: [PATCH v2 2/3] ata: pata_falcon: add data_swab option to byte-swap disk data

[Michael Schmitz <schmitzmic@gmail.com>]

Hi Finn,

Am 18.08.2023 um 19:43 schrieb Finn Thain:
>
> On Fri, 18 Aug 2023, Michael Schmitz wrote:
>
>> 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 v1:
>>
>> Damien Le Moal:
>> - change patch title
>> - drop swap_data flag
>>
>> Finn Thain:
>> - drop allocation of ap->private struct, use field as bitmask
>>
>> 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 | 10 +++++++++-
>>  1 file changed, 9 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/ata/pata_falcon.c b/drivers/ata/pata_falcon.c
>> index 346259e3bbc8..27443cb757de 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_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)");
>> +
>>  static const struct scsi_host_template pata_falcon_sht = {
>>  	ATA_PIO_SHT(DRV_NAME),
>>  };
>> @@ -46,11 +51,12 @@ static unsigned int pata_falcon_data_xfer(struct ata_queued_cmd *qc,
>>  	void __iomem *data_addr = ap->ioaddr.data_addr;
>>  	unsigned int words = buflen >> 1;
>>  	struct scsi_cmnd *cmd = qc->scsicmd;
>> +	int dev_id = dev->devno;
>
> Is that variable really needed?

Not really, no.

>
>>  	bool swap = 1;
>>
>>  	if (dev->class == ATA_DEV_ATA && cmd &&
>>  	    !blk_rq_is_passthrough(scsi_cmd_to_rq(cmd)))
>> -		swap = 0;
>> +		swap = (uintptr_t)ap->private_data & BIT(dev_id);
>>
>>  	/* Transfer multiple of 2 bytes */
>>  	if (rw == READ) {
>> @@ -199,6 +205,8 @@ 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 *)(uintptr_t)(pata_falcon_swap_mask >> (2 * pdev->id));
>> +
>
> My compiler doesn't need that extra type cast in there...

Geert's suggestion for 64 bit safety...

Cheers,

	Michael

>
>>  	irq_res = platform_get_resource(pdev, IORESOURCE_IRQ, 0);
>>  	if (irq_res && irq_res->start > 0) {
>>  		irq = irq_res->start;
>>