Re: [PATCH v8 7/7] drm: exynos: mixer: Add interconnect support

[Chanwoo Choi <cwchoi00@gmail.com>]

Hi Sylwester,

On Wed, Nov 4, 2020 at 7:37 PM Sylwester Nawrocki
<s.nawrocki@samsung.com> wrote:
>
> This patch adds interconnect support to exynos-mixer. The mixer works
> the same as before when CONFIG_INTERCONNECT is 'n'.
>
> For proper operation of the video mixer block we need to ensure the
> interconnect busses like DMC or LEFTBUS provide enough bandwidth so
> as to avoid DMA buffer underruns in the mixer block. I.e we need to
> prevent those busses from operating in low perfomance OPPs when
> the mixer is running.
> In this patch the bus bandwidth request is done through the interconnect
> API, the bandwidth value is calculated from selected DRM mode, i.e.
> video plane width, height, refresh rate and pixel format.
>
> The bandwidth setting is synchronized with VSYNC when we are switching
> to lower bandwidth. This is required to ensure enough bandwidth for
> the device since new settings are normally being applied in the hardware
> synchronously with VSYNC.
>
> Acked-by: Krzysztof Kozlowski <krzk@kernel.org>
> Co-developed-by: Artur Świgoń <a.swigon@samsung.com>
> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
> Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
> ---
> Changes for v8:
>  - updated comment in mixer_probe()
>
> Changes for v7:
>  - fixed incorrect setting of the ICC bandwidth when the mixer is
>    disabled, now the bandwidth is set explicitly to 0 in such case.
>
> Changes for v6:
>  - the icc_set_bw() call is now only done when calculated value for
>    a crtc changes, this avoids unnecessary calls per each video frame
>  - added synchronization of the interconnect bandwidth setting with
>    the mixer VSYNC in order to avoid buffer underflow when we lower
>    the interconnect bandwidth when the hardware still operates with
>    previous mode settings that require higher bandwidth. This fixed
>    IOMMU faults observed e.g. during switching from two planes to
>    a single plane operation.
>
> Changes for v5:
>  - renamed soc_path variable to icc_path
> ---
>  drivers/gpu/drm/exynos/exynos_mixer.c | 146 ++++++++++++++++++++++++++++++++--
>  1 file changed, 138 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/exynos/exynos_mixer.c b/drivers/gpu/drm/exynos/exynos_mixer.c
> index af192e5..8c1509e 100644
> --- a/drivers/gpu/drm/exynos/exynos_mixer.c
> +++ b/drivers/gpu/drm/exynos/exynos_mixer.c
> @@ -13,6 +13,7 @@
>  #include <linux/component.h>
>  #include <linux/delay.h>
>  #include <linux/i2c.h>
> +#include <linux/interconnect.h>
>  #include <linux/interrupt.h>
>  #include <linux/irq.h>
>  #include <linux/kernel.h>
> @@ -73,6 +74,7 @@ enum mixer_flag_bits {
>         MXR_BIT_INTERLACE,
>         MXR_BIT_VP_ENABLED,
>         MXR_BIT_HAS_SCLK,
> +       MXR_BIT_REQUEST_BW,
>  };
>
>  static const uint32_t mixer_formats[] = {
> @@ -99,6 +101,13 @@ struct mixer_context {
>         struct exynos_drm_plane planes[MIXER_WIN_NR];
>         unsigned long           flags;
>
> +       struct icc_path         *icc_path;
> +       /* memory bandwidth on the interconnect bus in B/s */
> +       unsigned long           icc_bandwidth;
> +       /* mutex protecting @icc_bandwidth */
> +       struct mutex            icc_lock;
> +       struct work_struct      work;
> +
>         int                     irq;
>         void __iomem            *mixer_regs;
>         void __iomem            *vp_regs;
> @@ -754,6 +763,9 @@ static irqreturn_t mixer_irq_handler(int irq, void *arg)
>                 val |= MXR_INT_CLEAR_VSYNC;
>                 val &= ~MXR_INT_STATUS_VSYNC;
>
> +               if (test_and_clear_bit(MXR_BIT_REQUEST_BW, &ctx->flags))
> +                       schedule_work(&ctx->work);
> +
>                 /* interlace scan need to check shadow register */
>                 if (test_bit(MXR_BIT_INTERLACE, &ctx->flags)
>                     && !mixer_is_synced(ctx))
> @@ -934,6 +946,76 @@ static void mixer_disable_vblank(struct exynos_drm_crtc *crtc)
>         mixer_reg_writemask(mixer_ctx, MXR_INT_EN, 0, MXR_INT_EN_VSYNC);
>  }
>
> +/**
> + * mixer_get_memory_bandwidth - calculate memory bandwidth for current crtc mode
> + * @crtc: a crtc with DRM mode to calculate the bandwidth for
> + *
> + * Return: memory bandwidth in B/s
> + *
> + * This function returns memory bandwidth calculated as a sum of amount of data
> + * per second for each plane. The calculation is based on maximum possible pixel
> + * resolution for a plane so as to avoid different bandwidth request per each
> + * video frame. The formula used for calculation for each plane is:
> + *
> + * bw = width * height * frame_rate / interlace / (hor_subs * vert_subs)
> + *
> + * where:
> + *  - width, height - (DRM mode) video frame width and height in pixels,
> + *  - frame_rate - DRM mode frame refresh rate,
> + *  - interlace: 1 - in case of progressive and 2 in case of interlaced video,
> + *  - hor_subs, vert_subs - accordingly horizontal and vertical pixel
> + *    subsampling for a plane.
> + */
> +static unsigned int mixer_get_memory_bandwidth(struct exynos_drm_crtc *crtc)
> +{
> +       struct drm_display_mode *mode = &crtc->base.state->adjusted_mode;
> +       struct mixer_context *ctx = crtc->ctx;
> +       unsigned long bw, bandwidth = 0;
> +       int i, j, sub;
> +
> +       for (i = 0; i < MIXER_WIN_NR; i++) {
> +               struct drm_plane *plane = &ctx->planes[i].base;
> +               const struct drm_format_info *format;
> +
> +               if (plane->state && plane->state->crtc && plane->state->fb) {
> +                       format = plane->state->fb->format;
> +                       bw = mode->hdisplay * mode->vdisplay *
> +                                                       drm_mode_vrefresh(mode);
> +                       if (mode->flags & DRM_MODE_FLAG_INTERLACE)
> +                               bw /= 2;
> +                       for (j = 0; j < format->num_planes; j++) {
> +                               sub = j ? (format->vsub * format->hsub) : 1;
> +                               bandwidth += format->cpp[j] * bw / sub;
> +                       }
> +               }
> +       }
> +
> +       return bandwidth;
> +}
> +
> +static void mixer_set_icc_bandwidth(struct mixer_context *ctx,
> +                                   unsigned long bandwidth)
> +{
> +       u32 avg_bw, peak_bw;
> +
> +       /* add 20% safety margin */
> +       bandwidth = bandwidth / 4 * 5;
> +
> +       avg_bw = peak_bw = Bps_to_icc(bandwidth);
> +       icc_set_bw(ctx->icc_path, avg_bw, peak_bw);
> +
> +       dev_dbg(ctx->dev, "safe bandwidth %lu Bps\n", bandwidth);
> +}
> +
> +static void mixer_icc_request_fn(struct work_struct *work)
> +{
> +       struct mixer_context *ctx = container_of(work, struct mixer_context,
> +                                                work);
> +       mutex_lock(&ctx->icc_lock);
> +       mixer_set_icc_bandwidth(ctx, ctx->icc_bandwidth);
> +       mutex_unlock(&ctx->icc_lock);
> +}
> +
>  static void mixer_atomic_begin(struct exynos_drm_crtc *crtc)
>  {
>         struct mixer_context *ctx = crtc->ctx;
> @@ -980,12 +1062,35 @@ static void mixer_disable_plane(struct exynos_drm_crtc *crtc,
>
>  static void mixer_atomic_flush(struct exynos_drm_crtc *crtc)
>  {
> -       struct mixer_context *mixer_ctx = crtc->ctx;
> +       struct mixer_context *ctx = crtc->ctx;
> +       int bw, prev_bw;
>
> -       if (!test_bit(MXR_BIT_POWERED, &mixer_ctx->flags))
> +       if (!test_bit(MXR_BIT_POWERED, &ctx->flags))
>                 return;
>
> -       mixer_enable_sync(mixer_ctx);
> +       /*
> +        * Request necessary bandwidth on the interconnects. If new
> +        * bandwidth is greater than current value set the new value
> +        * immediately. Otherwise request lower bandwidth only after
> +        * VSYNC, after the HW has actually switched to new video
> +        * frame settings.
> +        */
> +       if (ctx->icc_path) {
> +               bw = mixer_get_memory_bandwidth(crtc);
> +
> +               mutex_lock(&ctx->icc_lock);
> +               prev_bw = ctx->icc_bandwidth;
> +               ctx->icc_bandwidth = bw;
> +
> +               if (bw > prev_bw)
> +                       mixer_set_icc_bandwidth(ctx, bw);
> +               else if (bw < prev_bw)
> +                       set_bit(MXR_BIT_REQUEST_BW, &ctx->flags);
> +
> +               mutex_unlock(&ctx->icc_lock);
> +       }
> +
> +       mixer_enable_sync(ctx);
>         exynos_crtc_handle_event(crtc);
>  }
>
> @@ -1036,6 +1141,8 @@ static void mixer_atomic_disable(struct exynos_drm_crtc *crtc)
>
>         pm_runtime_put(ctx->dev);
>
> +       mixer_set_icc_bandwidth(ctx, 0);
> +
>         clear_bit(MXR_BIT_POWERED, &ctx->flags);
>  }
>
> @@ -1223,19 +1330,33 @@ static int mixer_probe(struct platform_device *pdev)
>         struct device *dev = &pdev->dev;
>         const struct mixer_drv_data *drv;
>         struct mixer_context *ctx;
> +       struct icc_path *path;
>         int ret;
>
> +       /*
> +        * Returns NULL if CONFIG_INTERCONNECT is disabled or if "interconnects"
> +        * property does not exist. May return ERR_PTR(-EPROBE_DEFER).
> +        */
> +       path = of_icc_get(dev, NULL);
> +       if (IS_ERR(path))
> +               return PTR_ERR(path);
> +
>         ctx = devm_kzalloc(&pdev->dev, sizeof(*ctx), GFP_KERNEL);
>         if (!ctx) {
>                 DRM_DEV_ERROR(dev, "failed to alloc mixer context.\n");
> -               return -ENOMEM;
> +               ret = -ENOMEM;
> +               goto err;
>         }
>
>         drv = of_device_get_match_data(dev);
>
> +       INIT_WORK(&ctx->work, mixer_icc_request_fn);
> +       mutex_init(&ctx->icc_lock);
> +
>         ctx->pdev = pdev;
>         ctx->dev = dev;
>         ctx->mxr_ver = drv->version;
> +       ctx->icc_path = path;
>
>         if (drv->is_vp_enabled)
>                 __set_bit(MXR_BIT_VP_ENABLED, &ctx->flags);
> @@ -1247,17 +1368,26 @@ static int mixer_probe(struct platform_device *pdev)
>         pm_runtime_enable(dev);
>
>         ret = component_add(&pdev->dev, &mixer_component_ops);
> -       if (ret)
> +       if (ret) {
>                 pm_runtime_disable(dev);
> -
> +               goto err;
> +       }
> +       return 0;
> +err:
> +       icc_put(path);
>         return ret;
>  }
>
>  static int mixer_remove(struct platform_device *pdev)
>  {
> -       pm_runtime_disable(&pdev->dev);
> +       struct device *dev = &pdev->dev;
> +       struct mixer_context *ctx = dev_get_drvdata(dev);
> +
> +       pm_runtime_disable(dev);
> +
> +       component_del(dev, &mixer_component_ops);
>
> -       component_del(&pdev->dev, &mixer_component_ops);
> +       icc_put(ctx->icc_path);
>
>         return 0;
>  }
> --
> 2.7.4
>
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Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>

-- 
Best Regards,
Chanwoo Choi