linux-kernel - Re: [PATCH 2/4] gpu: host1x: Enable gather filter

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Message-ID: <a39083bd-a51e-1070-a304-295bb22ad930@kapsi.fi>
Date:   Mon, 21 Aug 2017 20:28:16 +0300
From:   Mikko Perttunen <cyndis@...si.fi>
To:     Dmitry Osipenko <digetx@...il.com>,
        Mikko Perttunen <mperttunen@...dia.com>,
        thierry.reding@...il.com, jonathanh@...dia.com
Cc:     dri-devel@...ts.freedesktop.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] gpu: host1x: Enable gather filter



On 08/21/2017 08:27 PM, Mikko Perttunen wrote:
> 
> 
> On 08/20/2017 07:59 PM, Dmitry Osipenko wrote:
>> On 20.08.2017 19:44, Dmitry Osipenko wrote:
>>> On 20.08.2017 19:24, Dmitry Osipenko wrote:
>>>> On 18.08.2017 19:15, Mikko Perttunen wrote:
>>>>> The gather filter is a feature present on Tegra124 and newer where the
>>>>> hardware prevents GATHERed command buffers from executing commands
>>>>> normally reserved for the CDMA pushbuffer which is maintained by the
>>>>> kernel driver.
>>>>>
>>>>> This commit enables the gather filter on all supporting hardware.
>>>>>
>>>>> Signed-off-by: Mikko Perttunen <mperttunen@...dia.com>
>>>>> ---
>>>>>   drivers/gpu/host1x/hw/channel_hw.c          | 22 
>>>>> ++++++++++++++++++++++
>>>>>   drivers/gpu/host1x/hw/hw_host1x04_channel.h | 12 ++++++++++++
>>>>>   drivers/gpu/host1x/hw/hw_host1x05_channel.h | 12 ++++++++++++
>>>>>   3 files changed, 46 insertions(+)
>>>>>
>>>>> diff --git a/drivers/gpu/host1x/hw/channel_hw.c 
>>>>> b/drivers/gpu/host1x/hw/channel_hw.c
>>>>> index 0161da331702..5c0dc6bb51d1 100644
>>>>> --- a/drivers/gpu/host1x/hw/channel_hw.c
>>>>> +++ b/drivers/gpu/host1x/hw/channel_hw.c
>>>>> @@ -181,10 +181,32 @@ static int channel_submit(struct host1x_job 
>>>>> *job)
>>>>>       return err;
>>>>>   }
>>>>> +static void enable_gather_filter(struct host1x *host,
>>>>> +                 struct host1x_channel *ch)
>>>>> +{
>>>>> +#if HOST1X_HW >= 6
>>>>> +    u32 val;
>>>>> +
>>>>> +    if (!host->hv_regs)
>>>>> +        return;
>>>>
>>>> Is it really possible that gather filter could be not present on HW 
>>>> without
>>>> hypervisor? Maybe there is other way to enable it in that case?
> 
> The hardware may have the hypervisor but Linux may be running as a 
> virtual machine without access to the hypervisor, in which case we 
> cannot access the registers, and it's the responsibility of the other OS 
> acting as hypervisor to enable the gather filter.
> 
>>>>
>>>> Is possible at all that hypervisor could be missed?
>>>
>>> BTW, this is also incoherent with the 'syncpoint protection' patch 
>>> which doesn't
>>> check for hypervisor presence.
>>>
>>
>> However, I noticed that check and it's wrongly placed ;) See comment 
>> to the
>> 'syncpoint protection' patch.

Also - thanks, I added the missing check to that patch :)

>>
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