linux-kernel - Re: [RFC,v2,1/8] video: tegra: Add nvhost driver

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Date:	Mon, 10 Dec 2012 12:28:24 +0200
From:	Terje Bergström <tbergstrom@...dia.com>
To:	Mark Zhang <nvmarkzhang@...il.com>
CC:	"thierry.reding@...onic-design.de" <thierry.reding@...onic-design.de>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC,v2,1/8] video: tegra: Add nvhost driver

On 29.11.2012 11:10, Mark Zhang wrote:
>> +
>> +/**
>> + * Write a cpu syncpoint increment to the hardware, without touching
>> + * the cache. Caller is responsible for host being powered.
>> + */
>> +static void host1x_syncpt_cpu_incr(struct nvhost_syncpt *sp, u32 id)
>> +{
>> +     struct nvhost_master *dev = syncpt_to_dev(sp);
>> +     u32 reg_offset = id / 32;
>> +
>> +     if (!nvhost_module_powered(dev->dev)) {
>> +             dev_err(&syncpt_to_dev(sp)->dev->dev,
>> +                     "Trying to access host1x when it's off");
>> +             return;
>> +     }
>> +
>> +     if (!nvhost_syncpt_client_managed(sp, id)
>> +                     && nvhost_syncpt_min_eq_max(sp, id)) {
>> +             dev_err(&syncpt_to_dev(sp)->dev->dev,
>> +                     "Trying to increment syncpoint id %d beyond max\n",
>> +                     id);
>> +             return;
>> +     }
>> +     writel(BIT_MASK(id), dev->sync_aperture +
>> +                     host1x_sync_syncpt_cpu_incr_r() + reg_offset * 4);
> 
> I have a stupid question: According to the name and the context of this
> function, seems it increases the syncpt value which specified by param
> "id". So how does this "writel" increase the value? I don't know much
> about host1x/syncpt reg operations, so could you explain a little bit or
> I just completely have a wrong understanding?

I believe I've implemented most of the requests in this mail, but I seem
to have missed answering this question.

writel() to that register invokes a method in host1x, which increments
the sync point indicated by the value of the register by one.

Best regards,
Terje
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