Re: [PATCH/RFC 4/4] irq-pio: add read/write multiple support

[Albert Lee <albertcc@tw.ibm.com>]

Jeff,

> Mark Lord wrote:
>
>> Albert Lee wrote:
>>
>>> Patch 4/4: add read/write multiple support
>>>
>>
>> One "fine point" when programming the R/W MULT commands
>> is to remember that each register access is very costly
>> in terms of processor time.
>>
>> So whenever an access can be done with 28-bit LBA,
>> it should not use the EXT versions of the instructions,
>> even though the device may be LBA48 capable.
>>
>> The various drivers I have written for Linux and other OSs
>> that deal with this always logic equivalen to this somewhere:
>>
>> if (lba_sector < (1<<28) && sector_count <= 256) {
>>     use LBA28
>> } else if (device is lba48 capable) {
>>     use LBA48
>> } else {
>>     error
>> }
>
>
> Alan lists this on his PATA should-do list, too.
>
> Since this is legacy hardware, I am a bit skeptical about doing this 
> -- and also 32-bit PIO, which is in the same category -- because this 
> increases the amount of code we have to deal with, for the same basic 
> function.  For rarely-hit situations, I don't mind paying some 
> performance penalty if it reduces long term maintenance.  I am willing 
> to push some ancient platforms in the "slow but working" category, to 
> keep the code small and easier to review/debug/maintain.
>
> That said, it should be simple enough to push the logic into 
> libata-scsi.c, where it translates a SCSI READ/WRITE command into an 
> ATA read/write command.  Patches welcome...
>
I would like to work on the LBA28/LBA48 translation. Please withdraw the 
r/w multiple patch 4/4 for the moment since it might conflict with it.
Thanks.

Albert