Re: [PATCH] ide: Add tx4938ide driver

[Sergei Shtylyov <sshtylyov@ru.mvista.com>]

Hello.

Atsushi Nemoto wrote:

>>>+	/* IORDY setup time: 35ns */
>>>+	wt = (35 + cycle - 1) / cycle;

>>    It's not that simple I'm afraid: you can't just wait IORDY for 35 ns as 
>>that won't guarantee the minimum DIOx- actime time for the current PIO mode; 
>>so t->act8 (since it's >= t->act) should be part of the equation here, 
>>possibly with subtraction of couple cycles, if I'm interpreting the timing 
>>diagrams in the datasheet correctly...

> Hmm... so, does this statement seems correct?

> 	wt = (t->act8b + 35 + cycle - 1) / cycle - 2;

    No need to add the 35 ns since they're counted from the moment -DIOx gets 
asserted.  It would only make sense to check whether:

	wt = DIV_ROUND_UP(t->act8b, cycle) - 2;

is less than the 35 ns minimum, and use 35 ns if so:

	wt = max(DIV_ROUND_UP(t->act8b, cycle) - 2, DIV_ROUND_UP(35, cycle));

>>>+	/* actual wait-cycle is max(wt & ~1, 1) */

>>    I got an impression that WT[0] bit is used otherwise in the ready mode, 
>>and PWT[1:0]:WT[3:1] = 00000 would mean 0 cycles, not 1...

> From "7.3.6.3  Ready Mode":

> 	When the number of wait cycles is 0, READY check is started in
> 	1 cycle after asserting the CE* signal. When the number of
> 	wait cycles is other than zero, after waiting only for the
> 	specified number of cycles, READY check is started.

    Indeed, I've missed that...

MBR, Sergei