From: Kishon Vijay Abraham I <kishon@ti.com>
To: Tony Lindgren <tony@atomide.com>, Suman Anna <s-anna@ti.com>,
Paul Walmsley <paul@pwsan.com>,
Bjorn Helgaas <bhelgaas@google.com>
Cc: <richardcochran@gmail.com>, Russell King <linux@arm.linux.org.uk>,
<linux-omap@vger.kernel.org>,
<linux-arm-kernel@lists.infradead.org>,
<linux-kernel@vger.kernel.org>, <nsekhar@ti.com>
Subject: Re: [PATCH v3 3/3] pci: dra7xx: use pdata callbacks to perform reset
Date: Fri, 5 Feb 2016 09:49:55 +0530 [thread overview]
Message-ID: <56B422EB.5000603@ti.com> (raw)
In-Reply-To: <56B087AD.4000505@ti.com>
Hi Paul,
On Tuesday 02 February 2016 04:10 PM, Kishon Vijay Abraham I wrote:
> Hi,
>
> On Friday 29 January 2016 12:01 AM, Tony Lindgren wrote:
>> * Suman Anna <s-anna@ti.com> [160127 15:17]:
>>> On 01/27/2016 12:56 PM, Tony Lindgren wrote:
>>>> * Suman Anna <s-anna@ti.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.
>>
>> OK so if hwmod code has already done the reset, then why would you need
>> to deassert reset in the device driver probe?
>
> The hwmod code only asserts the reset lines and that is not enough to access
> the PCI registers. The reset lines must be de-asserted before accessing the
> PCIe registers.
>>
>>>> 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.
>
> right. I thought if some program like the bootloader requires the reset lines
> to be in initial hw state, then it might break on 'reboot'. So restored it back
> to the initial hw state.
>>
>> I don't understand this part either.. Usually you just power up and init
>> the registers to a sane state in a device driver probe and on exit just
>> power down the device.
>>
>>>>>> 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.
>>
>> OK if the hwmod code does not deassert reset lines properly on enable,
>> then that sounds like a bug that should be fixed instead of adding
>> device specific work arounds.
>
> I think some devices require the reset lines to be asserted and some devices
> require it to be de-asserted and hwmod was designed when there was only the
> first type of devices. I'm not sure though.
>>
>> Sorry to keep dragging this on a bit longer, but I think we need to
>> hear Paul's comments on this one.
>
> I agree.
> Paul, what do you think is the best way forward to perform reset?
Can you give your feedback as we are at the risk of PCIe driver being removed?
Thanks
Kishon
>
> Thanks
> Kishon
> --
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next prev parent reply other threads:[~2016-02-05 4:20 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-14 14:11 [PATCH v3 0/3] dra7xx: get pcie working in mainline Kishon Vijay Abraham I
2016-01-14 14:11 ` [PATCH v3 1/3] ARM: DRA7: hwmod: Add reset data for PCIe Kishon Vijay Abraham I
2016-02-08 1:50 ` Paul Walmsley
2016-01-14 14:11 ` [PATCH v3 2/3] ARM: DRA7: add pdata-quirks to do reset of PCIe Kishon Vijay Abraham I
2016-01-15 19:19 ` Suman Anna
2016-01-15 19:22 ` Tony Lindgren
2016-01-15 19:41 ` Suman Anna
2016-01-18 9:12 ` Sekhar Nori
2016-01-27 17:23 ` Tony Lindgren
2016-01-14 14:11 ` [PATCH v3 3/3] pci: dra7xx: use pdata callbacks to perform reset Kishon Vijay Abraham I
2016-01-27 17:31 ` Tony Lindgren
2016-01-27 18:16 ` Suman Anna
2016-01-27 18:56 ` Tony Lindgren
2016-01-27 23:16 ` Suman Anna
2016-01-28 18:31 ` Tony Lindgren
2016-01-28 21:15 ` Suman Anna
2016-02-02 10:40 ` Kishon Vijay Abraham I
2016-02-05 4:19 ` Kishon Vijay Abraham I [this message]
2016-02-08 2:48 ` Paul Walmsley
2016-02-08 20:56 ` Suman Anna
2016-02-09 8:49 ` Paul Walmsley
2016-02-09 17:40 ` Suman Anna
2016-02-09 19:36 ` Paul Walmsley
2016-02-10 1:42 ` Suman Anna
2016-02-10 5:38 ` Kishon Vijay Abraham I
2016-02-11 19:27 ` Paul Walmsley
2016-02-11 22:04 ` Suman Anna
2016-02-12 6:49 ` Kishon Vijay Abraham I
2016-02-12 17:20 ` Suman Anna
2016-02-18 14:21 ` Sekhar Nori
2016-02-18 17:23 ` Paul Walmsley
2016-02-18 18:27 ` Suman Anna
2016-02-22 6:18 ` Kishon Vijay Abraham I
2016-02-22 6:31 ` Paul Walmsley
2016-02-22 9:55 ` Kishon Vijay Abraham I
2016-02-23 11:57 ` Kishon Vijay Abraham I
2016-02-23 18:28 ` Paul Walmsley
2016-02-24 6:21 ` Kishon Vijay Abraham I
2016-03-01 8:25 ` Paul Walmsley
2016-03-01 11:55 ` Kishon Vijay Abraham I
2016-03-01 14:43 ` Bjorn Helgaas
2016-03-01 16:55 ` Suman Anna
2016-02-11 20:43 ` Suman Anna
2016-02-12 6:55 ` Kishon Vijay Abraham I
2016-02-10 5:36 ` Kishon Vijay Abraham I
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