Re: [PATCH v4 2/2] ata: pata_falcon: add data_swab option to byte-swap disk data

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

On 8/24/23 01:35, Sergey Shtylyov wrote:
> On 8/23/23 1:13 AM, 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>
>> Tested-by: William R Sowerbutts <will@sowerbutts.com>
>> Signed-off-by: Michael Schmitz <schmitzmic@gmail.com>
> 
> Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>
> 
> [...]
> 
>> diff --git a/drivers/ata/pata_falcon.c b/drivers/ata/pata_falcon.c
>> index 3841ea200bcb..7cf15bd9764a 100644
>> --- a/drivers/ata/pata_falcon.c
>> +++ b/drivers/ata/pata_falcon.c
> [...]
>> @@ -194,6 +199,9 @@ static int __init pata_falcon_init_one(struct platform_device *pdev)
>>  	ata_port_desc(ap, "cmd %px ctl %px data %pa",
>>  		      base, ctl_base, &ap->ioaddr.data_addr);
>>  
>> +	ap->private_data = (void *)(uintptr_t)(pdev->id > 0 ?
>> +		pata_falcon_swap_mask >> 2 : pata_falcon_swap_mask);
> 
>    How about:
> 
> 	ap->private_data = (void *)(uintptr_t)(pata_falcon_swap_mask >>
> 			   (pdev->id > 0 ? 2 : 0));

This is so hard to decode... Let's please spell this out.
Something like:

	int shift;

	if (pdev->id)
		shift = 2;
	else
		shift = 0;
	ap->private_data = (uintptr_t)(pata_falcon_swap_mask >> shift);

This is initialization, so no need to try to optimize and rather privilege clear
code.

> 
> [...]
> 
> MBR, Sergey

-- 
Damien Le Moal
Western Digital Research