Re: [PATCH v5 2/2] ata: pata_falcon: add data_swab option to byte-swap disk data

[Michael Schmitz <schmitzmic@gmail.com>]

Hi Geert,

Am 25.08.23 um 19:46 schrieb Geert Uytterhoeven:
> Hi Michael,
>
> On Fri, Aug 25, 2023 at 3:13 AM Michael Schmitz <schmitzmic@gmail.com> 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>
>> Tested-by: William R Sowerbutts <will@sowerbutts.com>
>> Signed-off-by: Michael Schmitz <schmitzmic@gmail.com>
>> Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>
>> Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
>>
>> ---
>>
>> Changes since v4:
>>
>> Damien Le Moal:
>> - spell out bitmask shift calculation
> Thanks for the update!
>
> Sorry to bother you again...
>
>> --- a/drivers/ata/pata_falcon.c
>> +++ b/drivers/ata/pata_falcon.c
>> @@ -124,7 +129,7 @@ static int __init pata_falcon_init_one(struct platform_device *pdev)
>>         struct ata_host *host;
>>         struct ata_port *ap;
>>         void __iomem *base, *ctl_base;
>> -       int irq = 0, io_offset = 1, reg_shift = 2; /* Falcon defaults */
>> +       int irq = 0, io_offset = 1, reg_shift = 2, mask_shift; /* Falcon defaults */
> The comment does not apply to the mask_shift variable, unless you
> pre-initialize it to 0...

It does not apply to mask_shift even then - '0' is the default for the
first Q40 ISA adapter also, not just for Falcon.

I'll move mask_shift to its own line so the comment can be correct.

>
>>         dev_info(&pdev->dev, "Atari Falcon and Q40/Q60 PATA controller\n");
>>
>> @@ -194,6 +199,12 @@ static int __init pata_falcon_init_one(struct platform_device *pdev)
>>         ata_port_desc(ap, "cmd %px ctl %px data %px",
>>                       base, ctl_base, ap->ioaddr.data_addr);
>>
>> +       if (pdev->id > 0)
>> +               mask_shift = 2;
>> +       else
>> +               mask_shift = 0;
> ... and drop the else.

Damien did seem quite partial to that one, so I'll leave it.

Cheers,

    Michael

>
>> +       ap->private_data = (void *)(uintptr_t)(pata_falcon_swap_mask >> mask_shift);
>> +
>>         irq_res = platform_get_resource(pdev, IORESOURCE_IRQ, 0);
>>         if (irq_res && irq_res->start > 0) {
>>                 irq = irq_res->start;
> Gr{oetje,eeting}s,
>
>                         Geert
>