linux-kernel - Re: [PATCH v3 3/3] pci: dra7xx: use pdata callbacks to perform reset

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Date:	Wed, 27 Jan 2016 17:16:07 -0600
From:	Suman Anna <s-anna@...com>
To:	Tony Lindgren <tony@...mide.com>
CC:	Kishon Vijay Abraham I <kishon@...com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	<richardcochran@...il.com>, Russell King <linux@....linux.org.uk>,
	<linux-omap@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <nsekhar@...com>
Subject: Re: [PATCH v3 3/3] pci: dra7xx: use pdata callbacks to perform reset

On 01/27/2016 12:56 PM, Tony Lindgren wrote:
> * Suman Anna <s-anna@...com> [160127 10:17]:
>> On 01/27/2016 11:31 AM, Tony Lindgren wrote:
>>> Why do you need another reset here? Can't you just implement PM runtime
>>> in the driver and do the usual pm_runtime_put_sync followed by
>>> pm_runtime_disable?
>>
>> The omap_hwmod_enable/disable code does not deal with hardresets (PRCM
>> reset lines) and so the pm_runtime_get_sync/put_sync only end up dealing
>> with clocks, and we need to invoke the reset functions separately.
>> Modules with softresets in SYSCONFIG are ok, as they are dealt with
>> properly.
> 
> Hmm _reset() in omap_hwmod.c has this to call _assert_hardreset:
> 
> 	if (oh->class->reset) {
> 		r = oh->class->reset(oh);
> 	} else {
> 		if (oh->rst_lines_cnt > 0) {
> 			for (i = 0; i < oh->rst_lines_cnt; i++)
> 				_assert_hardreset(oh, oh->rst_lines[i].name);
> 			return 0;
> 		} else {
> 			r = _ocp_softreset(oh);
> 			if (r == -ENOENT)
> 				r = 0;
> 		}
> 	}

Right, hwmod code does the initial reset.

> Care to explain what exactly the problem with the hwmod code not doing
> the reset on init?

And we only need to deassert the reset in probe. Technically, we don't
need to assert first and deassert in probe, and that was a design choice
made by Kishon.

> And why do you need to do another reset in dra7xx_pcie_remove()?

Primarily to restore the reset state back to what it was after the
driver remove gets called. We cannot call deassert twice without calling
a assert in between. Kishon had originally added the assert and deassert
only in probe, but nothing in remove, they ought to be deassert in probe
and assert in remove to match initial hardware state, and to also make
it work across multiple probe/remove.

>>> Basically I'm wondering how come we need these platform data callbacks
>>> at all.
>>
>> The hardresets are controlled through the
>> omap_device_assert(deassert)_hardreset functions, and since these are
>> limited to mach-omap2, we are invoking them through platform data callbacks.
> 
> Right.. But I'm wondering about the why you need to do this in the
> driver at all part :)

The initial reset at init time is okay, but hwmod _enable() bails out if
the resets lines are asserted. This was a change made long time back, I
believe to deal with the problems around the DSP enabling sequences. As
such, pm_runtime_get_sync() and put_sync() do not deassert and assert
the resets.

regards
Suman