linux-kernel - Re: [PATCH 2/3] venus: Limit HFI sessions to the maximum supported

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Date:   Fri, 20 Nov 2020 17:14:50 -0800
From:   Fritz Koenig <frkoenig@...omium.org>
To:     Stanimir Varbanov <stanimir.varbanov@...aro.org>
Cc:     linux-media@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Vikash Garodia <vgarodia@...eaurora.org>,
        Mansur Alisha Shaik <mansur@...eaurora.org>,
        Dikshita Agarwal <dikshita@...eaurora.org>
Subject: Re: [PATCH 2/3] venus: Limit HFI sessions to the maximum supported

On Thu, Nov 19, 2020 at 4:12 PM Stanimir Varbanov
<stanimir.varbanov@...aro.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@...aro.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;
> +
> +       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--;
>         }
>

My understanding of the hardware is that there is a max number of
macroblocks that can be worked on at a time.  That works out to
nominally 16 clips.  But large clips can take more resources.  Does
|max_sessions_supported| get updated with the amount that system can
use?  Or is it always a constant?

If it changes depending on system load, then couldn't
|core->max_sessions_supported| be 0 if all of the resources have been
used up?  If that is the case then the below check would appear to be
incorrect.

> +       if (!core->max_sessions_supported)
> +               core->max_sessions_supported = MAX_SESSIONS;
> +
>         parser_fini(inst, codecs, domain);
>
>         return HFI_ERR_NONE;
> --
> 2.17.1
>