linux-kernel - Re: [Nouveau] [PATCH 06/12] drm/nouveau/ibus: add GK20A support

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Date:	Wed, 2 Apr 2014 23:22:43 +0900
From:	Alexandre Courbot <gnurou@...il.com>
To:	Ilia Mirkin <imirkin@...m.mit.edu>
Cc:	Thierry Reding <thierry.reding@...il.com>,
	"nouveau@...ts.freedesktop.org" <nouveau@...ts.freedesktop.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	Ben Skeggs <bskeggs@...hat.com>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [Nouveau] [PATCH 06/12] drm/nouveau/ibus: add GK20A support

On Wed, Apr 2, 2014 at 11:18 PM, Ilia Mirkin <imirkin@...m.mit.edu> wrote:
> On Wed, Apr 2, 2014 at 9:52 AM, Alexandre Courbot <gnurou@...il.com> wrote:
>> On Tue, Mar 25, 2014 at 7:34 AM, Thierry Reding
>> <thierry.reding@...il.com> wrote:
>>> On Mon, Mar 24, 2014 at 05:42:28PM +0900, Alexandre Courbot wrote:
>>> [...]
>>>> diff --git a/drivers/gpu/drm/nouveau/core/subdev/ibus/nvea.c b/drivers/gpu/drm/nouveau/core/subdev/ibus/nvea.c
>>> [...]
>>>> +#include <subdev/ibus.h>
>>>> +
>>>> +struct nvea_ibus_priv {
>>>> +     struct nouveau_ibus base;
>>>> +};
>>>> +
>>>> +static void
>>>> +nvea_ibus_init_priv_ring(struct nvea_ibus_priv *priv)
>>>> +{
>>>> +     nv_mask(priv, 0x137250, 0x3f, 0);
>>>> +
>>>> +     nv_mask(priv, 0x000200, 0x20, 0);
>>>> +     udelay(20);
>>>
>>> usleep_range()?
>>
>> Sure.
>>
>>>
>>>> +static void
>>>> +nvea_ibus_intr(struct nouveau_subdev *subdev)
>>>> +{
>>> [...]
>>>> +     /* Acknowledge interrupt */
>>>> +     nv_mask(priv, 0x12004c, 0x2, 0x2);
>>>> +
>>>> +     while (--retry >= 0) {
>>>> +             command = nv_rd32(priv, 0x12004c) & 0x3f;
>>>> +             if (command == 0)
>>>> +                     break;
>>>> +     }
>>>> +
>>>> +     if (retry < 0)
>>>> +             nv_warn(priv, "timeout waiting for ringmaster ack\n");
>>>> +}
>>>
>>> Perhaps I'm being paranoid, but this loop now depends on the frequency
>>> of the various clocks involved and therefore might break at some point
>>> if the frequencies get sufficiently high.
>>>
>>> So a slightly safer implementation would use a proper timeout using a
>>> combination of msecs_to_jiffies(), time_before() and usleep_range(),
>>> like so:
>>>
>>>         timeout = jiffies + msecs_to_jiffies(...);
>>>
>>>         while (time_before(jiffies, timeout)) {
>>>                 command = nv_rd32(...) & 0x3f;
>>>                 if (command == 0)
>>>                         break;
>>>
>>>                 usleep_range(...);
>>>         }
>>>
>>>         if (time_after(jiffies, timeout))
>>>                 nv_warn(...);
>>
>> Right, now that I look at this code again I don't even understand why
>> I left it this way. Maybe I left some early test code slip into the
>> final patch, sorry about that.
>
> I just remembered about this, but there's also the nv_wait() macro,
> which you could use, e.g.
>
> if (!nv_wait(subdev, 0x12004c, 0x3f, 0x00))
>   nv_warn(...)
>
> It has built-in timeout logic/etc (although no sleeps in the middle).
> It does use the timer subdev, so if that's not operational at this
> point, you can't use it.

IBUS comes after TIMER in the nv_subdev_type enum, so I guess that
should work. Will try this solution, thanks!
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