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Subject: Re: [PATCH 2/3] venus: Limit HFI sessions to the maximum supported
To:     Alexandre Courbot <acourbot@chromium.org>
Cc:     linux-media@vger.kernel.org, linux-arm-msm@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Vikash Garodia <vgarodia@codeaurora.org>,
        Mansur Alisha Shaik <mansur@codeaurora.org>,
        Dikshita Agarwal <dikshita@codeaurora.org>
References: <20201120001037.10032-1-stanimir.varbanov@linaro.org>
 <20201120001037.10032-3-stanimir.varbanov@linaro.org>
 <CAPBb6MUnXmtSKy9NwikYXjafgB+WM9TKEFjkYK16T2V7KRx=JQ@mail.gmail.com>
From:   Stanimir Varbanov <stanimir.varbanov@linaro.org>
Message-ID: <8c6231b2-61c2-d432-aa47-ddc29de8da19@linaro.org>
Date:   Wed, 25 Nov 2020 15:01:01 +0200
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On 11/25/20 5:46 AM, Alexandre Courbot wrote:
> On Fri, Nov 20, 2020 at 9:12 AM Stanimir Varbanov
> <stanimir.varbanov@linaro.org> wrote:
>>
>> Currently we rely on firmware to return error when we reach the maximum
>> supported number of sessions. But this errors are happened at reqbuf
>> time which is a bit later. The more reasonable way looks like is to
>> return the error on driver open.
>>
>> To achieve that modify hfi_session_create to return error when we reach
>> maximum count of sessions and thus refuse open.
>>
>> Signed-off-by: Stanimir Varbanov <stanimir.varbanov@linaro.org>
>> ---
>>  drivers/media/platform/qcom/venus/core.h      |  1 +
>>  drivers/media/platform/qcom/venus/hfi.c       | 19 +++++++++++++++----
>>  .../media/platform/qcom/venus/hfi_parser.c    |  3 +++
>>  3 files changed, 19 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/media/platform/qcom/venus/core.h b/drivers/media/platform/qcom/venus/core.h
>> index db0e6738281e..3a477fcdd3a8 100644
>> --- a/drivers/media/platform/qcom/venus/core.h
>> +++ b/drivers/media/platform/qcom/venus/core.h
>> @@ -96,6 +96,7 @@ struct venus_format {
>>  #define MAX_CAP_ENTRIES                32
>>  #define MAX_ALLOC_MODE_ENTRIES 16
>>  #define MAX_CODEC_NUM          32
>> +#define MAX_SESSIONS           16
>>
>>  struct raw_formats {
>>         u32 buftype;
>> diff --git a/drivers/media/platform/qcom/venus/hfi.c b/drivers/media/platform/qcom/venus/hfi.c
>> index 638ed5cfe05e..8420be6d3991 100644
>> --- a/drivers/media/platform/qcom/venus/hfi.c
>> +++ b/drivers/media/platform/qcom/venus/hfi.c
>> @@ -175,6 +175,7 @@ static int wait_session_msg(struct venus_inst *inst)
>>  int hfi_session_create(struct venus_inst *inst, const struct hfi_inst_ops *ops)
>>  {
>>         struct venus_core *core = inst->core;
>> +       int ret;
>>
>>         if (!ops)
>>                 return -EINVAL;
>> @@ -183,12 +184,22 @@ int hfi_session_create(struct venus_inst *inst, const struct hfi_inst_ops *ops)
>>         init_completion(&inst->done);
>>         inst->ops = ops;
>>
>> -       mutex_lock(&core->lock);
>> -       list_add_tail(&inst->list, &core->instances);
>> -       atomic_inc(&core->insts_count);
>> +       ret = mutex_lock_interruptible(&core->lock);
>> +       if (ret)
>> +               return ret;
> 
> Why do we change to mutex_lock_interruptible() here? This makes this

Because mutex_lock_interruptible is preferable in kernel docs, but I
agree that changing mutex_lock with mutex_lock_interruptible should be
subject of another lock related patches. I will drop this in next patch
version.

> function return an error even though we could obtain the lock just by
> trying a bit harder.

I didn't get that. The behavior of mutex_lock_interruptible is that same
as mutex_lock, i.e. the it will sleep to acquire the lock. The
difference is that the sleep could be interrupted by a signal. You might
think about mutex_trylock?

> 
>> +
>> +       ret = atomic_read(&core->insts_count);
>> +       if (ret + 1 > core->max_sessions_supported) {
>> +               ret = -EAGAIN;
>> +       } else {
>> +               atomic_inc(&core->insts_count);
>> +               list_add_tail(&inst->list, &core->instances);
>> +               ret = 0;
>> +       }
>> +
>>         mutex_unlock(&core->lock);
>>
>> -       return 0;
>> +       return ret;
>>  }
>>  EXPORT_SYMBOL_GPL(hfi_session_create);
>>
>> diff --git a/drivers/media/platform/qcom/venus/hfi_parser.c b/drivers/media/platform/qcom/venus/hfi_parser.c
>> index 363ee2a65453..52898633a8e6 100644
>> --- a/drivers/media/platform/qcom/venus/hfi_parser.c
>> +++ b/drivers/media/platform/qcom/venus/hfi_parser.c
>> @@ -276,6 +276,9 @@ u32 hfi_parser(struct venus_core *core, struct venus_inst *inst, void *buf,
>>                 words_count--;
>>         }
>>
>> +       if (!core->max_sessions_supported)
>> +               core->max_sessions_supported = MAX_SESSIONS;
>> +
>>         parser_fini(inst, codecs, domain);
>>
>>         return HFI_ERR_NONE;
>> --
>> 2.17.1
>>

-- 
regards,
Stan