linux-kernel - Re: [PATCH v14 2/4] CMDQ: Mediatek CMDQ driver

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Message-ID: <1475226691.13398.35.camel@mtksdaap41>
Date:   Fri, 30 Sep 2016 17:11:31 +0800
From:   CK Hu <ck.hu@...iatek.com>
To:     Horng-Shyang Liao <hs.liao@...iatek.com>
CC:     Rob Herring <robh+dt@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Jassi Brar <jassisinghbrar@...il.com>,
        "Daniel Kurtz" <djkurtz@...omium.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-mediatek@...ts.infradead.org>,
        <srv_heupstream@...iatek.com>,
        Sascha Hauer <kernel@...gutronix.de>,
        "Philipp Zabel" <p.zabel@...gutronix.de>,
        Nicolas Boichat <drinkcat@...omium.org>,
        cawa cheng <cawa.cheng@...iatek.com>,
        Bibby Hsieh <bibby.hsieh@...iatek.com>,
        YT Shen <yt.shen@...iatek.com>,
        Daoyuan Huang <daoyuan.huang@...iatek.com>,
        Damon Chu <damon.chu@...iatek.com>,
        "Josh-YC Liu" <josh-yc.liu@...iatek.com>,
        Glory Hung <glory.hung@...iatek.com>,
        Jiaguang Zhang <jiaguang.zhang@...iatek.com>,
        Dennis-YC Hsieh <dennis-yc.hsieh@...iatek.com>,
        Monica Wang <monica.wang@...iatek.com>
Subject: Re: [PATCH v14 2/4] CMDQ: Mediatek CMDQ driver

Hi, HS:

One comment inline

On Fri, 2016-09-30 at 16:56 +0800, Horng-Shyang Liao wrote:
> Hi CK,
> 
> Please see my inline reply.
> 
> On Fri, 2016-09-30 at 11:06 +0800, CK Hu wrote:
> > Hi, HS:
> > 
> > On Mon, 2016-09-05 at 09:44 +0800, HS Liao wrote:
> > > This patch is first version of Mediatek Command Queue(CMDQ) driver. The
> > > CMDQ is used to help write registers with critical time limitation,
> > > such as updating display configuration during the vblank. It controls
> > > Global Command Engine (GCE) hardware to achieve this requirement.
> > > Currently, CMDQ only supports display related hardwares, but we expect
> > > it can be extended to other hardwares for future requirements.
> > > 
> > > Signed-off-by: HS Liao <hs.liao@...iatek.com>
> > > Signed-off-by: CK Hu <ck.hu@...iatek.com>
> > > ---
> > 
> > [snip...]
> > 
> > > +
> > > +struct cmdq_task {
> > > +	struct cmdq		*cmdq;
> > > +	struct list_head	list_entry;
> > > +	void			*va_base;
> > > +	dma_addr_t		pa_base;
> > > +	size_t			cmd_buf_size; /* command occupied size */
> > > +	size_t			buf_size; /* real buffer size */
> > > +	bool			finalized;
> > > +	struct cmdq_thread	*thread;
> > 
> > I think thread info could be removed from cmdq_task. Only
> > cmdq_task_handle_error() and cmdq_task_insert_into_thread() use
> > task->thread and caller of both function has the thread info. So you
> > could just pass thread info into these two function and remove thread
> > info in cmdq_task.
> 
> This modification will remove 1 pointer but add 2 pointers. Moreover,
> more pointers will need to be delivered between functions for future
> extension. IMHO, it would be better to keep thread pointer inside
> cmdq_task.
> 
> > > +	struct cmdq_task_cb	cb;
> > 
> > I think this callback function is equal to mailbox client tx_done
> > callback. It's better to use already-defined interface rather than
> > creating your own.
> 
> This is because CMDQ driver allows different callback functions for
> different tasks, but mailbox only allows one callback function per
> channel. But, I think I can add a wrapper for tx_done to call CMDQ
> callback functions. So, I will use tx_done in CMDQ v15.

Up to now, one callback function for one channel is enough for DRM. So
'different callback function for different sent-message' looks like an
advanced function. Maybe you should not include it in first patch. 

Regards,
CK

> 
> > > +};
> > > +
> > 
> > [snip...]
> > 
> > > +
> > > +static int cmdq_suspend(struct device *dev)
> > > +{
> > > +	struct cmdq *cmdq = dev_get_drvdata(dev);
> > > +	struct cmdq_thread *thread;
> > > +	int i;
> > > +	bool task_running = false;
> > > +
> > > +	mutex_lock(&cmdq->task_mutex);
> > > +	cmdq->suspended = true;
> > > +	mutex_unlock(&cmdq->task_mutex);
> > > +
> > > +	for (i = 0; i < ARRAY_SIZE(cmdq->thread); i++) {
> > > +		thread = &cmdq->thread[i];
> > > +		if (!list_empty(&thread->task_busy_list)) {
> > > +			mod_timer(&thread->timeout, jiffies + 1);
> > > +			task_running = true;
> > > +		}
> > > +	}
> > > +
> > > +	if (task_running) {
> > > +		dev_warn(dev, "exist running task(s) in suspend\n");
> > > +		msleep(20);
> > 
> > Why sleep here? It looks like a recovery but could 20ms recovery
> > something? I think warning message is enough because you see the warning
> > message, and you fix the bug, so no need to recovery anything.
> 
> My purpose is context switch to finish timer's work.
> I will replace it by schedule().
> 
> > > +	}
> > > +
> > > +	clk_unprepare(cmdq->clock);
> > > +	return 0;
> > > +}
> > > +
> > 
> > Regards,
> > CK
> 
> Thanks,
> HS
> 
>