Re: [RESEND RFC/PATCH 6/8] media: platform: mtk-vcodec: Add Mediatek V4L2 Video Encoder Driver

From: Daniel Thompson
Date: Mon Nov 30 2015 - 09:58:21 EST

On 30 November 2015 at 11:39, tiffany lin <tiffany.lin@xxxxxxxxxxxx> wrote:
>> > diff --git a/drivers/media/platform/mtk-vcodec/Makefile b/drivers/media/platform/mtk-vcodec/Makefile
>> > new file mode 100644
>> > index 0000000..c7f7174
>> > --- /dev/null
>> > +++ b/drivers/media/platform/mtk-vcodec/Makefile
>> > @@ -0,0 +1,12 @@
>> > +obj-$(CONFIG_VIDEO_MEDIATEK_VCODEC) += mtk_vcodec_intr.o \
>> > + mtk_vcodec_util.o \
>> > + mtk_vcodec_enc_drv.o \
>> > + mtk_vcodec_enc.o \
>> > + mtk_vcodec_enc_pm.o
>> > +
>> > +obj-$(CONFIG_VIDEO_MEDIATEK_VCODEC) += common/
>> > +
>> > +ccflags-y += -I$(srctree)/drivers/media/platform/mtk-vcodec/include \
>> > + -I$(srctree)/drivers/media/platform/mtk-vcodec \
>> > + -I$(srctree)/drivers/media/platform/mtk-vpu
>>
>> Seems like there's a lot of directories here. Are these files
>> (framework, common, vcodec, etc) so unrelated they really need to live
>> in separate directories?
>>
>> Why not just drivers/media/platform/mediatek?
> This is because VPU and Vcodec are two different drivers.
> Driver in mtk-vpu is for controlling VPU device and provide
> communication API to VPU.
> Driver in mtk-vcodec is for control different encoder (vp8, h264), it
> include v4l2 driver layer, glue layer between encoders and vp8 and h264
> encoder.

They may be separate pieces of hardware the drivers for them are very
clearly interlinked. This is obvious because the Makefiles are having
to set ccflags to pick up the headers of the other drivers.

No other V4L2 driver uses ccflags-y in this manner.


>> > diff --git a/drivers/media/platform/mtk-vcodec/common/Makefile b/drivers/media/platform/mtk-vcodec/common/Makefile
>> > new file mode 100644
>> > index 0000000..477ab80
>> > --- /dev/null
>> > +++ b/drivers/media/platform/mtk-vcodec/common/Makefile
>> > @@ -0,0 +1,8 @@
>> > +obj-y += \
>> > + venc_drv_if.o
>> > +
>> > +ccflags-y += \
>> > + -I$(srctree)/include/ \
>> > + -I$(srctree)/drivers/media/platform/mtk-vcodec \
>> > + -I$(srctree)/drivers/media/platform/mtk-vcodec/include \
>> > + -I$(srctree)/drivers/media/platform/mtk-vpu
>>
>> As above, this appears to be a directory to hold just one file.
>>
> Sorry, I didn't get it. Could you explain more?

Just that this is another example of the excessive directory structure.

A directory that contains only one source file is a strong indication
that the splitting of the V4L2 implementation into directories is
excessive.


>> > diff --git a/drivers/media/platform/mtk-vcodec/common/venc_drv_if.c
>> b/drivers/media/platform/mtk-vcodec/common/venc_drv_if.c
>> > new file mode 100644
>> > index 0000000..9b3f025
>> > --- /dev/null
>> > +++ b/drivers/media/platform/mtk-vcodec/common/venc_drv_if.c
>> > @@ -0,0 +1,152 @@
>> > +/*
>> > + * Copyright (c) 2015 MediaTek Inc.
>> > + * Author: Daniel Hsiao <daniel.hsiao@xxxxxxxxxxxx>
>> > + * Jungchang Tsao <jungchang.tsao@xxxxxxxxxxxx>
>> > + *
>> > + * This program is free software; you can redistribute it and/or
>> > + * modify
>> > + * it under the terms of the GNU General Public License version 2 as
>> > + * published by the Free Software Foundation.
>> > + *
>> > + * This program is distributed in the hope that it will be useful,
>> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
>> > + * GNU General Public License for more details.
>> > + */
>> > +
>> > +#include <linux/interrupt.h>
>> > +#include <linux/kernel.h>
>> > +#include <linux/slab.h>
>> > +
>> > +#include "mtk_vcodec_drv.h"
>> > +#include "mtk_vcodec_enc.h"
>> > +#include "mtk_vcodec_pm.h"
>> > +#include "mtk_vcodec_util.h"
>> > +#include "mtk_vpu_core.h"
>> > +
>> > +#include "venc_drv_if.h"
>> > +#include "venc_drv_base.h"
>> > +
>> > +
>> > +int venc_if_create(void *ctx, unsigned int fourcc, unsigned long
>> *handle)
>> > +{
>> > + struct venc_handle *h;
>> > + char str[10];
>> > +
>> > + mtk_vcodec_fmt2str(fourcc, str);
>> > +
>> > + h = kzalloc(sizeof(*h), GFP_KERNEL);
>> > + if (!h)
>> > + return -ENOMEM;
>> > +
>> > + h->fourcc = fourcc;
>> > + h->ctx = ctx;
>> > + mtk_vcodec_debug(h, "fmt = %s handle = %p", str, h);
>> > +
>> > + switch (fourcc) {
>> > + default:
>> > + mtk_vcodec_err(h, "invalid format %s", str);
>> > + goto err_out;
>> > + }
>> > +
>> > + *handle = (unsigned long)h;
>> > + return 0;
>> > +
>> > +err_out:
>> > + kfree(h);
>> > + return -EINVAL;
>> > +}
>> > +
>> > +int venc_if_init(unsigned long handle)
>> > +{
>> > + int ret = 0;
>> > + struct venc_handle *h = (struct venc_handle *)handle;
>> > +
>> > + mtk_vcodec_debug_enter(h);
>> > +
>> > + mtk_venc_lock(h->ctx);
>> > + mtk_vcodec_enc_clock_on();
>> > + vpu_enable_clock(vpu_get_plat_device(h->ctx->dev->plat_dev));
>> > + ret = h->enc_if->init(h->ctx, (unsigned long *)&h->drv_handle);
>> > + vpu_disable_clock(vpu_get_plat_device(h->ctx->dev->plat_dev));
>> > + mtk_vcodec_enc_clock_off();
>> > + mtk_venc_unlock(h->ctx);
>> > +
>> > + return ret;
>> > +}
>>
>> To me this looks more like an obfuscation layer rather than a
>> abstraction layer. I don't understand why we need to hide things from
>> the V4L2 implementation that this code forms part of.
>>
>> More importantly, if this code was included somewhere where it could be
>> properly integrated with the device model you might be able to use the
>> pm_runtime system to avoid this sort of "heroics" to manage the clocks
>> anyway.
>>
> We want to abstract common part from encoder driver.
> Every encoder driver follow same calling flow and only need to take care
> about how to communicate with vpu to encode specific format.
> Encoder driver do not need to take care clock and multiple instance
> issue.

Looking at each of those stages:

mtk_venc_lock():
Why isn't one of the existing V4L2 locking strategies ok for you?

mtk_vcodec_enc_clock_on():
This does seem like something a sub-driver *should* be doing for itself

vpu_enable_clock():
Why can't the VPU driver manage this internally using pm_runtime?


That is why I described this as an obfuscation layer. It is collecting
a bunch of stuff that can be handled using the kernel driver model and
clumping them together in a special middle layer.


>> > +/**
>> > + * enum mtk_instance_type - The type of an MTK Vcodec instance.
>> > + */
>> > +enum mtk_instance_type {
>> > + MTK_INST_DECODER = 0,
>> > + MTK_INST_ENCODER = 1,
>> > +};
>> > +
>> > +/**
>> > + * enum mtk_instance_state - The state of an MTK Vcodec instance.
>> > + * @MTK_STATE_FREE - default state when instance create
>> > + * @MTK_STATE_CREATE - vdec instance is create
>> > + * @MTK_STATE_INIT - vdec instance is init
>> > + * @MTK_STATE_CONFIG - reserved for encoder
>> > + * @MTK_STATE_HEADER - vdec had sps/pps header parsed
>> > + * @MTK_STATE_RUNNING - vdec is decoding
>> > + * @MTK_STATE_FLUSH - vdec is flushing
>> > + * @MTK_STATE_RES_CHANGE - vdec detect resolution change
>> > + * @MTK_STATE_FINISH - ctx instance is stopped streaming
>> > + * @MTK_STATE_DEINIT - before release ctx instance
>> > + * @MTK_STATE_ERROR - vdec has something wrong
>> > + * @MTK_STATE_ABORT - abort work in working thread
>> > + */
>> > +enum mtk_instance_state {
>> > + MTK_STATE_FREE = 0,
>> > + MTK_STATE_CREATE = (1 << 0),
>> > + MTK_STATE_INIT = (1 << 1),
>> > + MTK_STATE_CONFIG = (1 << 2),
>> > + MTK_STATE_HEADER = (1 << 3),
>> > + MTK_STATE_RUNNING = (1 << 4),
>> > + MTK_STATE_FLUSH = (1 << 5),
>> > + MTK_STATE_RES_CHANGE = (1 << 6),
>> > + MTK_STATE_FINISH = (1 << 7),
>> > + MTK_STATE_DEINIT = (1 << 8),
>> > + MTK_STATE_ERROR = (1 << 9),
>> > + MTK_STATE_ABORT = (1 << 10),
>>
>> This looks like it started as a state machine and somehow turned into
>> flags, resulting in a state machine with 2048 states or, to give it a
>> different name, a debugging nightmare.
>>
> It's define some state happened rather than state machine.
> Though some states are for v4l2 decoder driver and not used in encoder
> driver.

Saying the flags track when "something happened" doesn't stop this
from being an extremely complex (and poorly documented) state machine.

There are way too many states compared to what is needed to implement
V4L2 correctly. To make clear why I am raising this point: with the
current driver state management code it is close to impossible to
properly review the error paths in this driver. The cause of error and
the recovery after error are too decoupled.


>> If the start streaming operation implemented cleanup-on-error properly
>> then there would only be two useful states: Started and stopped. Even
>> the "sticky" error behavior looks unnecessary to me (meaning we don't
>> need to track its state).
>>
> We cannot guaranteed that IOCTLs called from the user space follow
> required sequence.
> We need states to know if our driver could accept IOCTL command.

I believe that knowing whether the streaming is started or stopped
(e.g. two states) is sufficient for a driver to correctly handle
abitrary ioctls from userspace and even then, the core code tracks
this state for you so there's no need for you do it.

The queue/dequeue ioctls succeed or fail based on the length of the
queue (i.e. is the buffer queue overflowing or not) and have no need
to check the streaming state.

If you are absolutely sure that the other states are needed then
please provide an example of an ioctl() sequence where the additional
state is needed.


>> > diff --git a/drivers/media/platform/mtk-vcodec/mtk_vcodec_enc.c b/drivers/media/platform/mtk-vcodec/mtk_vcodec_enc.c
>> > new file mode 100644
>> > index 0000000..8e1b6f0
>> > --- /dev/null
>> > +++ b/drivers/media/platform/mtk-vcodec/mtk_vcodec_enc.c
>> > @@ -0,0 +1,1773 @@
>> > [...]
>> > +static int vb2ops_venc_start_streaming(struct vb2_queue *q, unsigned int count)
>> > +{
>> > + struct mtk_vcodec_ctx *ctx = vb2_get_drv_priv(q);
>> > + struct v4l2_device *v4l2_dev = &ctx->dev->v4l2_dev;
>> > + int ret;
>> > +#if MTK_V4L2_BENCHMARK
>> > + struct timeval begin, end;
>> > +
>> > + do_gettimeofday(&begin);
>> > +#endif
>> > +
>> > + if (!(vb2_start_streaming_called(&ctx->m2m_ctx->out_q_ctx.q) &
>> > + vb2_start_streaming_called(&ctx->m2m_ctx->cap_q_ctx.q))) {
>> > + mtk_v4l2_debug(1, "[%d]-> out=%d cap=%d",
>> > + ctx->idx,
>> > + vb2_start_streaming_called(&ctx->m2m_ctx->out_q_ctx.q),
>> > + vb2_start_streaming_called(&ctx->m2m_ctx->cap_q_ctx.q));
>> > + return 0;
>> > + }
>> > +
>> > + if ((ctx->state & (MTK_STATE_ERROR | MTK_STATE_ABORT)))
>> > + return -EINVAL;
>>
>> This is the sort of thing I mean.
>>
>> This sticky error behaviour means that every subsequent call to
>> vb2ops_venc_start_streaming() will fail. Note also that the user will
>> never try to stop streaming (which can clear the error state) because
>> according to the return code it got when it tried to start streaming we
>> never actually started.
>>
>> This is what I mean about having two many states. From the user's
>> perspective there are only two states. There needs to be a good reason
>> for the driver to manage so many extra secret states internally.
>>
> For my understanding, that vb2ops_venc_start_streaming cannot fail.

I disagree: See
http://lxr.free-electrons.com/source/include/media/videobuf2-core.h#L288

How did you confirm your understanding before replying?

When this function returns an error the simplest (and easiest to
review) error recovery strategy is simply to undo any actions which
have already been performed (like resource allocation) and return an
error code.#

There is no need for the driver to remember that it has already
reported an error. If the userspace tries again then its OK for us to
fail again.


> If it fail, user space will close and release this encoder instance
> (fd).

The userspace is not required to do this and the driver must not
assume that it will. It could attempt some kind of reconfiguration and
retry.


> We really need to state driver to see what it should do when receive
> current IOCTL.

I think you'll find that the v4l2-core does this for you.


>> > +
>> > + if (ctx->state == MTK_STATE_FREE) {
>> > + ret = venc_if_create(ctx,
>> > + ctx->q_data[MTK_Q_DATA_DST].fmt->fourcc,
>> > + &ctx->h_enc);
>> > +
>> > + if (ret != 0) {
>> > + ctx->state |= MTK_STATE_ERROR;
>> > + v4l2_err(v4l2_dev, "invalid codec type=%x\n",
>> > + ctx->q_data[MTK_Q_DATA_DST].fmt->fourcc);
>> > + v4l2_err(v4l2_dev, "venc_if_create failed=%d\n", ret);
>> > + return -EINVAL;
>> > + }
>> > +
>> > + if (ctx->q_data[MTK_Q_DATA_DST].fmt->fourcc ==
>> > + V4L2_PIX_FMT_H264)
>> > + ctx->hdr = 1;
>> > +
>> > + ctx->state |= MTK_STATE_CREATE;
>> > + }
>> > +
>> > + if ((ctx->state & MTK_STATE_CREATE) && !(ctx->state & MTK_STATE_INIT)) {
>> > + ret = venc_if_init(ctx->h_enc);
>> > + if (ret != 0) {
>> > + ctx->state |= MTK_STATE_ERROR;
>> > + v4l2_err(v4l2_dev, "venc_if_init failed=%d\n", ret);
>> > + return -EINVAL;
>>
>> This error path leaves the encoder partially constructed and relies on
>> something else to tidy things up. It would be much better to tidy things
>> up from this function and
>>
>> Also I don't think both venc_if_create and venc_if_init are needed. They
>> are only ever called one after the other and thus they only serve to
>> complicate the error handling code.
>>
> venc_if_create is for creating instance in arm side and base on encode
> format hook corresponding encoder driver interface.
> venc_if_init is trying to init encoder instance in VPU side.
> Failures from two functions should have different error handling.
> We will enhance this part in next version.

As mentioned above, I'm very uncomfortable about this API in its
entirety and think it should be reconsidered.

So whilst I disagree here (the caller does not have any significant
difference in error handling so using -ENOMEM/-EINVAL/-EIO should be
quite sufficient to distringuish between errors) I rather you spent
some time trying to eliminate this API.


>> > diff --git a/drivers/media/platform/mtk-vcodec/mtk_vcodec_util.h b/drivers/media/platform/mtk-vcodec/mtk_vcodec_util.h
>> > new file mode 100644
>> > index 0000000..a8e683a
>> > --- /dev/null
>> > +++ b/drivers/media/platform/mtk-vcodec/mtk_vcodec_util.h
>> > @@ -0,0 +1,66 @@
>> > +/*
>> > +* Copyright (c) 2015 MediaTek Inc.
>> > +* Author: PC Chen <pc.chen@xxxxxxxxxxxx>
>> > +* Tiffany Lin <tiffany.lin@xxxxxxxxxxxx>
>> > +*
>> > +* This program is free software; you can redistribute it and/or modify
>> > +* it under the terms of the GNU General Public License version 2 as
>> > +* published by the Free Software Foundation.
>> > +*
>> > +* This program is distributed in the hope that it will be useful,
>> > +* but WITHOUT ANY WARRANTY; without even the implied warranty of
>> > +* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
>> > +* GNU General Public License for more details.
>> > +*/
>> > +
>> > +#ifndef _MTK_VCODEC_UTIL_H_
>> > +#define _MTK_VCODEC_UTIL_H_
>> > +
>> > +#include <linux/types.h>
>> > +#include <linux/dma-direction.h>
>> > +
>> > +struct mtk_vcodec_mem {
>> > + size_t size;
>> > + void *va;
>> > + dma_addr_t dma_addr;
>> > +};
>> > +
>> > +extern int mtk_v4l2_dbg_level;
>> > +extern bool mtk_vcodec_dbg;
>> > +
>> > +#define mtk_v4l2_debug(level, fmt, args...) \
>> > + do { \
>> > + if (mtk_v4l2_dbg_level >= level) \
>> > + pr_info("[MTK_V4L2] level=%d %s(),%d: " fmt "\n",\
>> > + level, __func__, __LINE__, ##args); \
>> > + } while (0)
>> > +
>> > +#define mtk_v4l2_err(fmt, args...) \
>> > + pr_err("[MTK_V4L2][ERROR] %s:%d: " fmt "\n", __func__, __LINE__, \
>> > + ##args)
>>
>> Obviously the code should be structured to make use of dev_dbg/dev_err
>> possible.
>>
>> However where this won't work do you really need special macros for
>> this. Assuming your error messages are well written 'git grep' and the
>> following should be enough:
>>
>> #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
>>
> Thanks.
> For pr_err case, we will try to use "#define pr_fmt(fmt) KBUILD_MODNAME
> ": " fmt" in next version.
> For pr_info case, we still need debug level to control output messages.

To be honest I expect new code to be able to rely on -DDEBUG and/or
CONFIG_DYNAMIC_DEBUG.

I really can't see why a single V4L2 driver needs to hand roll a six
level debug message framework. If it really, really, really needs it
then it should at least have the good manners to copy the prior art in
the existing V4L2 drivers.



>
>>
>> > +#define mtk_v4l2_debug_enter() mtk_v4l2_debug(5, "+\n")
>> > +#define mtk_v4l2_debug_leave() mtk_v4l2_debug(5, "-\n")
>>
>> Remove these. If you care about function entry and exit for debugging
>> you should be able to use ftrace.
>>
> I am not familiar with ftrace.
> What if we only want to trace v4l2 video encoder driver called flow not
> called stack? And only for functions we are interested not all
> functions.
> I will check if it is convenience for us using ftrace.

It is find for ftrace to only track a subset of functions.


Daniel.
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