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Re: [RESEND RFC/PATCH 3/8] media: platform: mtk-vpu: Support Mediatek VPU

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On Fri, 2015-11-27 at 12:21 +0000, Daniel Thompson wrote:
> On 27/11/15 12:10, andrew-ct chen wrote:
> >>> +
> >>> > >+	memcpy((void *)send_obj->share_buf, buf, len);
> >>> > >+	send_obj->len = len;
> >>> > >+	send_obj->id = id;
> >>> > >+	vpu_cfg_writel(vpu, 0x1, HOST_TO_VPU);
> >>> > >+
> >>> > >+	/* Wait until VPU receives the command */
> >>> > >+	timeout = jiffies + msecs_to_jiffies(IPI_TIMEOUT_MS);
> >>> > >+	do {
> >>> > >+		if (time_after(jiffies, timeout)) {
> >>> > >+			dev_err(vpu->dev, "vpu_ipi_send: IPI timeout!\n");
> >>> > >+			return -EIO;
> >>> > >+		}
> >>> > >+	} while (vpu_cfg_readl(vpu, HOST_TO_VPU));
> >> >
> >> >Do we need to busy wait every time we communicate with the co-processor?
> >> >Couldn't we put this wait*before*  we write to HOST_TO_VPU above.
> >> >
> >> >That way we only spin when there is a need to.
> >> >
> > Since the hardware VPU only allows that one client sends the command to
> > it each time.
> > We need the wait to make sure VPU accepted the command and cleared the
> > interrupt and then the next command would be served.
> 
> I understand that the VPU  can only have on message outstanding at once.
> 
> I just wonder why we busy wait *after* sending the first command rather 
> than *before* sending the second one.

No other special reasons. Just send one command and wait until VPU gets
the command. Then, I think this wait also can be put before we write to
HOST_TO_VPU.Is this better than former? May I know the reason?


> 
> Streamed decode/encode typically ends up being rate controlled by 
> capture or display meaning that in these cases we don't need to busy 
> wait at all (because by the time we send the next frame the VPU has 
> already accepted the previous message).

For now, only one device "encoder" exists, it is true.
But, we'll have encoder and decoder devices, the decode and encode
requested to VPU are simultaneous.
Is this supposed to be removed for this patches and we can add it back
if the another device(decoder) is ready for review?


Andrew


> 
> 
> Daniel.
> 
> 
> _______________________________________________
> Linux-mediatek mailing list
> Linux-mediatek@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-mediatek


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[RESEND RFC/PATCH 0/8] Add MT8173 Video Encoder Driver and VPU Driver Tiffany Lin <tiffany.lin@mediatek.com> - 2015-11-17 14:00 +0100
  [RESEND RFC/PATCH 1/8] dt-bindings: Add a binding for Mediatek Video Processor Unit Tiffany Lin <tiffany.lin@mediatek.com> - 2015-11-17 14:00 +0100
    Re: [RESEND RFC/PATCH 1/8] dt-bindings: Add a binding for Mediatek  Video Processor Unit Mark Rutland <mark.rutland@arm.com> - 2015-11-17 15:20 +0100
      Re: [RESEND RFC/PATCH 1/8] dt-bindings: Add a binding for Mediatek  Video Processor Unit andrew-ct chen <andrew-ct.chen@mediatek.com> - 2015-11-19 03:50 +0100
  [RESEND RFC/PATCH 2/8] arm64: dts: mediatek: Add node for Mediatek Video Processor Unit Tiffany Lin <tiffany.lin@mediatek.com> - 2015-11-17 14:00 +0100
  [RESEND RFC/PATCH 8/8] media: platform: mtk-vcodec: Add Mediatek H264 Video Encoder Driver Tiffany Lin <tiffany.lin@mediatek.com> - 2015-11-17 14:00 +0100
  [RESEND RFC/PATCH 4/8] dt-bindings: Add a binding for Mediatek Video Encoder Tiffany Lin <tiffany.lin@mediatek.com> - 2015-11-17 14:00 +0100
    Re: [RESEND RFC/PATCH 4/8] dt-bindings: Add a binding for Mediatek  Video Encoder Rob Herring <robh@kernel.org> - 2015-11-17 20:50 +0100
      Re: [RESEND RFC/PATCH 4/8] dt-bindings: Add a binding for Mediatek  Video Encoder tiffany lin <tiffany.lin@mediatek.com> - 2015-11-18 08:20 +0100
  [RESEND RFC/PATCH 5/8] arm64: dts: mediatek: Add Video Encoder for MT8173 Tiffany Lin <tiffany.lin@mediatek.com> - 2015-11-17 14:00 +0100
  Re: [RESEND RFC/PATCH 0/8] Add MT8173 Video Encoder Driver and VPU  Driver Hans Verkuil <hverkuil@xs4all.nl> - 2015-11-19 08:50 +0100
  Re: [RESEND RFC/PATCH 3/8] media: platform: mtk-vpu: Support Mediatek  VPU Daniel Thompson <daniel.thompson@linaro.org> - 2015-11-27 13:30 +0100
    Re: [RESEND RFC/PATCH 3/8] media: platform: mtk-vpu: Support  Mediatek VPU andrew-ct chen <andrew-ct.chen@mediatek.com> - 2015-11-30 12:50 +0100
      Re: [RESEND RFC/PATCH 3/8] media: platform: mtk-vpu: Support Mediatek VPU Daniel Thompson <daniel.thompson@linaro.org> - 2015-11-30 16:40 +0100
        Re: [RESEND RFC/PATCH 3/8] media: platform: mtk-vpu: Support  Mediatek VPU andrew-ct chen <andrew-ct.chen@mediatek.com> - 2015-12-01 15:40 +0100
  Re: [RESEND RFC/PATCH 6/8] media: platform: mtk-vcodec: Add Mediatek  V4L2 Video Encoder Driver Daniel Thompson <daniel.thompson@linaro.org> - 2015-11-27 17:40 +0100
    Re: [RESEND RFC/PATCH 6/8] media: platform: mtk-vcodec: Add  Mediatek V4L2 Video Encoder Driver tiffany lin <tiffany.lin@mediatek.com> - 2015-11-30 12:50 +0100
      Re: [RESEND RFC/PATCH 6/8] media: platform: mtk-vcodec: Add Mediatek  V4L2 Video Encoder Driver Daniel Thompson <daniel.thompson@linaro.org> - 2015-11-30 16:00 +0100
        Re: [RESEND RFC/PATCH 6/8] media: platform: mtk-vcodec: Add  Mediatek V4L2 Video Encoder Driver tiffany lin <tiffany.lin@mediatek.com> - 2015-12-01 11:50 +0100
          Re: [RESEND RFC/PATCH 6/8] media: platform: mtk-vcodec: Add Mediatek  V4L2 Video Encoder Driver Daniel Thompson <daniel.thompson@linaro.org> - 2015-12-01 16:50 +0100
            Re: [RESEND RFC/PATCH 6/8] media: platform: mtk-vcodec: Add  Mediatek V4L2 Video Encoder Driver tiffany lin <tiffany.lin@mediatek.com> - 2015-12-02 14:10 +0100
              Re: [RESEND RFC/PATCH 6/8] media: platform: mtk-vcodec: Add Mediatek  V4L2 Video Encoder Driver Daniel Thompson <daniel.thompson@linaro.org> - 2015-12-02 17:10 +0100

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