Re: [PATCH] libata: share PIO limits among devices sharing a channel

[Jeff Garzik <jgarzik@pobox.com>]

Alan wrote:
> On Thu, 25 Jan 2007 20:29:47 +0900
> Tejun Heo <htejun@gmail.com> wrote:
> 
>> PIO xfermask limits should be shared by all devices on the same
>> channel to avoid violating device selection timing.  libata used to
> 
> NAK, this is totally wrong
> 
>> +	/* PIO xfermask limits are shared by all devices on the same
>> +	 * channel to avoid violating device selection timing.
>> +	 */
>> +	for (i = 0; i < ATA_MAX_DEVICES; i++) {
>> +		struct ata_device *d = &ap->device[i];
>> +		unsigned int pio_mask;
>> +
>> +		if (ata_dev_absent(d))
>> +			continue;
>> +
>> +		ata_unpack_xfermask(ata_id_xfermask(d->id),
>> +				    &pio_mask, NULL, NULL);
>> +		pio_mask &= d->pio_mask;
>> +		xfer_mask &= ata_pack_xfermask(pio_mask, UINT_MAX, UINT_MAX);
>> +	}
> 
> NAK
> 
> This "guarantee" was deliberately removed long ago and is completely
> bogus.
> 
> The good ATA chipsets do not suffer from selection timing limits of this
> form. The less smart ones do and the drivers correctly merge the timing

Agreed.

I'm curious what the motivation of this patch was?

	Jeff