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From:   Alexandre Courbot <acourbot@chromium.org>
Date:   Fri, 6 Mar 2020 16:50:25 +0900
Message-ID: <CAPBb6MW-zxK+=HHUP5=+pO4Mswkhm=hDX7V56ABDm+BCzDaGHg@mail.gmail.com>
Subject: Re: [PATCH] venus: avoid extra locking in driver
To:     Mansur Alisha Shaik <mansur@codeaurora.org>
Cc:     Linux Media Mailing List <linux-media@vger.kernel.org>,
        Stanimir Varbanov <stanimir.varbanov@linaro.org>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-arm-msm@vger.kernel.org,
        Vikash Garodia <vgarodia@codeaurora.org>
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On Fri, Mar 6, 2020 at 2:34 PM Mansur Alisha Shaik
<mansur@codeaurora.org> wrote:
>
> This change will avoid extra locking in driver.

Could you elaborate a bit more on the problem that this patch solves?

>
> Signed-off-by: Mansur Alisha Shaik <mansur@codeaurora.org>
> ---
>  drivers/media/platform/qcom/venus/core.c       |  2 +-
>  drivers/media/platform/qcom/venus/core.h       |  2 +-
>  drivers/media/platform/qcom/venus/helpers.c    | 11 +++++++++--
>  drivers/media/platform/qcom/venus/pm_helpers.c |  8 ++++----
>  4 files changed, 15 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/media/platform/qcom/venus/core.c b/drivers/media/platform/qcom/venus/core.c
> index 194b10b9..75d38b8 100644
> --- a/drivers/media/platform/qcom/venus/core.c
> +++ b/drivers/media/platform/qcom/venus/core.c
> @@ -447,7 +447,7 @@ static const struct freq_tbl sdm845_freq_table[] = {
>         {  244800, 100000000 }, /* 1920x1080@30 */
>  };
>
> -static struct codec_freq_data sdm845_codec_freq_data[] =  {
> +static const struct codec_freq_data sdm845_codec_freq_data[] =  {
>         { V4L2_PIX_FMT_H264, VIDC_SESSION_TYPE_ENC, 675, 10 },
>         { V4L2_PIX_FMT_HEVC, VIDC_SESSION_TYPE_ENC, 675, 10 },
>         { V4L2_PIX_FMT_VP8, VIDC_SESSION_TYPE_ENC, 675, 10 },
> diff --git a/drivers/media/platform/qcom/venus/core.h b/drivers/media/platform/qcom/venus/core.h
> index ab7c360..8c8d0e9 100644
> --- a/drivers/media/platform/qcom/venus/core.h
> +++ b/drivers/media/platform/qcom/venus/core.h
> @@ -245,7 +245,7 @@ struct venus_buffer {
>  struct clock_data {
>         u32 core_id;
>         unsigned long freq;
> -       const struct codec_freq_data *codec_freq_data;
> +       struct codec_freq_data codec_freq_data;
>  };
>
>  #define to_venus_buffer(ptr)   container_of(ptr, struct venus_buffer, vb)
> diff --git a/drivers/media/platform/qcom/venus/helpers.c b/drivers/media/platform/qcom/venus/helpers.c
> index bcc6038..550c4ff 100644
> --- a/drivers/media/platform/qcom/venus/helpers.c
> +++ b/drivers/media/platform/qcom/venus/helpers.c
> @@ -807,6 +807,7 @@ int venus_helper_init_codec_freq_data(struct venus_inst *inst)
>         unsigned int i, data_size;
>         u32 pixfmt;
>         int ret = 0;
> +       bool found = false;
>
>         if (!IS_V4(inst->core))
>                 return 0;
> @@ -816,16 +817,22 @@ int venus_helper_init_codec_freq_data(struct venus_inst *inst)
>         pixfmt = inst->session_type == VIDC_SESSION_TYPE_DEC ?
>                         inst->fmt_out->pixfmt : inst->fmt_cap->pixfmt;
>
> +       memset(&inst->clk_data.codec_freq_data, 0,
> +               sizeof(inst->clk_data.codec_freq_data));
> +
>         for (i = 0; i < data_size; i++) {
>                 if (data[i].pixfmt == pixfmt &&
>                     data[i].session_type == inst->session_type) {
> -                       inst->clk_data.codec_freq_data = &data[i];
> +                       inst->clk_data.codec_freq_data = data[i];

From the patch I'd infer that inst->clk_data.codec_freq_data needs to
change at runtime. Is this what happens? Why? I'd expect that
frequency tables remain constant, and thus that the global
sdm845_codec_freq_data can remain constant while
clock_data::codec_freq_data is a const reference to it. What prevents
this from happening?

> +                       found = true;
>                         break;
>                 }
>         }
>
> -       if (!inst->clk_data.codec_freq_data)
> +       if (!found) {
> +               dev_err(inst->core->dev, "cannot find codec freq data\n");
>                 ret = -EINVAL;
> +       }
>
>         return ret;
>  }
> diff --git a/drivers/media/platform/qcom/venus/pm_helpers.c b/drivers/media/platform/qcom/venus/pm_helpers.c
> index abf9315..240845e 100644
> --- a/drivers/media/platform/qcom/venus/pm_helpers.c
> +++ b/drivers/media/platform/qcom/venus/pm_helpers.c
> @@ -496,7 +496,7 @@ min_loaded_core(struct venus_inst *inst, u32 *min_coreid, u32 *min_load)
>         list_for_each_entry(inst_pos, &core->instances, list) {
>                 if (inst_pos == inst)
>                         continue;
> -               vpp_freq = inst_pos->clk_data.codec_freq_data->vpp_freq;
> +               vpp_freq = inst_pos->clk_data.codec_freq_data.vpp_freq;
>                 coreid = inst_pos->clk_data.core_id;
>
>                 mbs_per_sec = load_per_instance(inst_pos);
> @@ -545,7 +545,7 @@ static int decide_core(struct venus_inst *inst)
>                 return 0;
>
>         inst_load = load_per_instance(inst);
> -       inst_load *= inst->clk_data.codec_freq_data->vpp_freq;
> +       inst_load *= inst->clk_data.codec_freq_data.vpp_freq;
>         max_freq = core->res->freq_tbl[0].freq;
>
>         min_loaded_core(inst, &min_coreid, &min_load);
> @@ -848,10 +848,10 @@ static unsigned long calculate_inst_freq(struct venus_inst *inst,
>
>         mbs_per_sec = load_per_instance(inst) / fps;
>
> -       vpp_freq = mbs_per_sec * inst->clk_data.codec_freq_data->vpp_freq;
> +       vpp_freq = mbs_per_sec * inst->clk_data.codec_freq_data.vpp_freq;
>         /* 21 / 20 is overhead factor */
>         vpp_freq += vpp_freq / 20;
> -       vsp_freq = mbs_per_sec * inst->clk_data.codec_freq_data->vsp_freq;
> +       vsp_freq = mbs_per_sec * inst->clk_data.codec_freq_data.vsp_freq;
>
>         /* 10 / 7 is overhead factor */
>         if (inst->session_type == VIDC_SESSION_TYPE_ENC)
> --
> 2.7.4
>