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

[Damien Le Moal <dlemoal@kernel.org>]

On 8/26/23 09:44, Michael Schmitz wrote:
> 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.

I am OK with mask_shift initialized to 0 when declared.
So whichever you prefer is fine.
What I do not like is the use of "?" instead of the easier to read plain "if" :)

> 
> 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
>>
> 

-- 
Damien Le Moal
Western Digital Research