[PATCH v3 1/5] reset: Add reset_reset() and reset_reset_bulk() API

[Michal Simek]

On 5/18/26 15:40, Maarten Brock wrote:
> Hello Michal,
> 
>> From: Michal Simek <michal.simek at amd.com>
>> On 5/18/26 14:07, Maarten Brock wrote:
>>>> From: Michal Simek <michal.simek at amd.com>
>>>> On 5/18/26 12:21, Maarten Brock wrote:
>>>>
>>>> I expect you would like to do it like this right?
>>>>
>>>> int reset_reset_bulk(struct reset_ctl_bulk *bulk, ulong delay_us)
>>>> {
>>>> 	int ret;
>>>>
>>>> 	ret = reset_assert_bulk(bulk);
>>>> 	if (ret) {
>>>> 		dev_err(bus, "Failed to assert reset: %d\n", ret);
>>>> 		return ret;
>>>> 	}
>>>>
>>>> 	udelay(delay_us);
>>>>
>>>> 	/* Deassert all OSPI reset lines */
>>>> 	ret = reset_deassert_bulk(bulk);
>>>> 	if (ret) {
>>>> 		dev_err(bus, "Failed to deassert reset: %d\n", ret);
>>>> 		return ret;
>>>> 	}
>>>>
>>>> 	return 0;
>>>> }
>>>
>>> That is correct.
>>> And a single delay of delay_us takes less time than N*delay_us (for N>1), so the total startup time is smaller (a.k.a. faster startup).
>>
>> It really depends on other factors and delay time. In our case it is not just
>> MMIO access. But it is SMC to TF-A and then seconding request over mailbox to
>> another firmware to ack it first and then do it. And with above you would have
>> to do twice compare to once.
>>
>> I can do another optimization which is that if bulk->count is 1 then call
>> reset_reset() directly and for others do what you see above.
>>
>> What do you think?
> 
> I very much doubt that all sorts of actions and compares will ever take more time than 1 us, unless some serial protocol is involved (uart/spi/i2c).
> So, I expect that delay_us is always the dominant elapsed time. And N*delay_us even more so.
> 
> I do understand that if the delay is handled by rst_reset() and underlying hardware, things might be different.
> So special handling of bulk->count=1 or *all* bulk resets are handled by rst_reset() could be a good idea.
> 
> How about something like this?
> 
> int reset_reset_bulk(struct reset_ctl_bulk *bulk, ulong delay_us)
> {
> 	int i, ret, soft = 0;
> 
> 	for (i = 0; i < bulk->count; i++) {
> 		struct reset_ops *ops = reset_dev_ops(bulk->resets[i].dev);
> 
> 		if (ops->rst_reset) {
> 			ret = ops->rst_reset(&bulk->resets[i], delay_us);
> 		} else {
> 			ret = reset_assert(&bulk->resets[i]);
> 			soft++;

But this will have weird behavior when you have multiple reset controllers where 
one has rst_reset implemented and another not. Then on that one with rst_reset 
another deassert is going to be called.

Thanks,
Michal