linux-kernel - Re: [RFC PATCH v6 6/9] media: tegra: Add Tegra210 Video input driver

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Date:   Mon, 6 Apr 2020 08:35:43 -0700
From:   Sowjanya Komatineni <skomatineni@...dia.com>
To:     Dmitry Osipenko <digetx@...il.com>, <thierry.reding@...il.com>,
        <jonathanh@...dia.com>, <frankc@...dia.com>, <hverkuil@...all.nl>,
        <sakari.ailus@....fi>, <helen.koike@...labora.com>
CC:     <sboyd@...nel.org>, <linux-media@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-clk@...r.kernel.org>,
        <linux-tegra@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v6 6/9] media: tegra: Add Tegra210 Video input driver


On 4/5/20 1:35 PM, Dmitry Osipenko wrote:
> External email: Use caution opening links or attachments
>
>
> 04.04.2020 04:25, Sowjanya Komatineni пишет:
> ...
>> +static int tegra_channel_capture_frame(struct tegra_vi_channel *chan,
>> +                                    struct tegra_channel_buffer *buf)
>> +{
>> +     int err = 0;
>> +     u32 thresh, value, frame_start, mw_ack_done;
>> +     int bytes_per_line = chan->format.bytesperline;
>> +
>> +     /* program buffer address by using surface 0 */
>> +     vi_csi_write(chan, TEGRA_VI_CSI_SURFACE0_OFFSET_MSB,
>> +                  (u64)buf->addr >> 32);
>> +     vi_csi_write(chan, TEGRA_VI_CSI_SURFACE0_OFFSET_LSB, buf->addr);
>> +     vi_csi_write(chan, TEGRA_VI_CSI_SURFACE0_STRIDE, bytes_per_line);
>> +
>> +     /*
>> +      * Tegra VI block interacts with host1x syncpt for synchronizing
>> +      * programmed condition of capture state and hardware operation.
>> +      * Frame start and Memory write acknowledge syncpts has their own
>> +      * FIFO of depth 2.
>> +      *
>> +      * Syncpoint trigger conditions set through VI_INCR_SYNCPT register
>> +      * are added to HW syncpt FIFO and when the HW triggers, syncpt
>> +      * condition is removed from the FIFO and counter at syncpoint index
>> +      * will be incremented by the hardware and software can wait for
>> +      * counter to reach threshold to synchronize capturing frame with the
>> +      * hardware capture events.
>> +      */
>> +
>> +     /* increase channel syncpoint threshold for FRAME_START */
>> +     thresh = host1x_syncpt_incr_max(chan->frame_start_sp, 1);
>> +
>> +     /* Program FRAME_START trigger condition syncpt request */
>> +     frame_start = VI_CSI_PP_FRAME_START(chan->portno);
>> +     value = VI_CFG_VI_INCR_SYNCPT_COND(frame_start) |
>> +             host1x_syncpt_id(chan->frame_start_sp);
>> +     tegra_vi_write(chan, TEGRA_VI_CFG_VI_INCR_SYNCPT, value);
>> +
>> +     /* increase channel syncpoint threshold for MW_ACK_DONE */
>> +     buf->mw_ack_sp_thresh = host1x_syncpt_incr_max(chan->mw_ack_sp, 1);
>> +
>> +     /* Program MW_ACK_DONE trigger condition syncpt request */
>> +     mw_ack_done = VI_CSI_MW_ACK_DONE(chan->portno);
>> +     value = VI_CFG_VI_INCR_SYNCPT_COND(mw_ack_done) |
>> +             host1x_syncpt_id(chan->mw_ack_sp);
>> +     tegra_vi_write(chan, TEGRA_VI_CFG_VI_INCR_SYNCPT, value);
>> +
>> +     /* enable single shot capture */
>> +     vi_csi_write(chan, TEGRA_VI_CSI_SINGLE_SHOT, SINGLE_SHOT_CAPTURE);
>> +     chan->capture_reqs++;
>> +
>> +     /* wait for syncpt counter to reach frame start event threshold */
>> +     err = host1x_syncpt_wait(chan->frame_start_sp, thresh,
>> +                              TEGRA_VI_SYNCPT_WAIT_TIMEOUT, &value);
>> +     if (err) {
>> +             dev_err(&chan->video.dev,
>> +                     "frame start syncpt timeout: %d\n", err);
>> +             /* increment syncpoint counter for timedout events */
>> +             host1x_syncpt_incr(chan->frame_start_sp);
> Why incrementing is done while hardware is still active?
>
> The sync point's state needs to be completely reset after resetting
> hardware. But I don't think that the current upstream host1x driver
> supports doing that, it's one of the known-long-standing problems of the
> host1x driver.
>
> At least the sp->max_val incrementing should be done based on the actual
> syncpoint value and this should be done after resetting hardware.

upstream host1x driver don't have API to reset or to equalize max value 
with min/load value.

So to synchronize missed event, incrementing HW syncpt counter.

This should not impact as we increment this in case of missed events only.

>> +             spin_lock(&chan->sp_incr_lock);
>> +             host1x_syncpt_incr(chan->mw_ack_sp);
>> +             spin_unlock(&chan->sp_incr_lock);
>> +             /* clear errors and recover */
>> +             tegra_channel_capture_error_recover(chan);
>> +             release_buffer(chan, buf, VB2_BUF_STATE_ERROR);
>> +             return err;
>> +     }