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Subject: Re: [PATCH v25 2/2] soc: mediatek: Add Mediatek CMDQ helper
From:   houlong wei <houlong.wei@mediatek.com>
To:     Matthias Brugger <matthias.bgg@gmail.com>
CC:     Jassi Brar <jassisinghbrar@gmail.com>,
        Rob Herring <robh+dt@kernel.org>,
        Daniel Kurtz <djkurtz@chromium.org>,
        Sascha Hauer <s.hauer@pengutronix.de>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
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        <linux-arm-kernel@lists.infradead.org>,
        "linux-mediatek@lists.infradead.org" 
        <linux-mediatek@lists.infradead.org>,
        srv_heupstream <srv_heupstream@mediatek.com>,
        Sascha Hauer <kernel@pengutronix.de>,
        Philipp Zabel <p.zabel@pengutronix.de>,
        "Nicolas Boichat" <drinkcat@chromium.org>,
        CK Hu =?UTF-8?Q?=28=E8=83=A1=E4=BF=8A=E5=85=89=29?= 
        <ck.hu@mediatek.com>,
        "Bibby Hsieh =?UTF-8?Q?=28=E8=AC=9D=E6=BF=9F=E9=81=A0=29?=" 
        <Bibby.Hsieh@mediatek.com>,
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        <Yt.Shen@mediatek.com>,
        Daoyuan Huang =?UTF-8?Q?=28=E9=BB=83=E9=81=93=E5=8E=9F=29?= 
        <Daoyuan.Huang@mediatek.com>,
        Jiaguang Zhang =?UTF-8?Q?=28=E5=BC=A0=E5=8A=A0=E5=B9=BF=29?= 
        <Jiaguang.Zhang@mediatek.com>,
        Dennis-YC Hsieh =?UTF-8?Q?=28=E8=AC=9D=E5=AE=87=E5=93=B2=29?= 
        <Dennis-YC.Hsieh@mediatek.com>,
        Monica Wang =?UTF-8?Q?=28=E7=8E=8B=E5=AD=9F=E5=A9=B7=29?= 
        <monica.wang@mediatek.com>,
        Hs Liao =?UTF-8?Q?=28=E5=BB=96=E5=AE=8F=E7=A5=A5=29?= 
        <Hs.Liao@mediatek.com>,
        Ginny Chen =?UTF-8?Q?=28=E9=99=B3=E6=B2=BB=E5=82=91=29?= 
        <ginny.chen@mediatek.com>,
        Enzhu Wang =?UTF-8?Q?=28=E7=8E=8B=E6=81=A9=E6=9F=B1=29?= 
        <enzhu.wang@mediatek.com>, <houlong.wei@mediatek.com>
Date:   Mon, 8 Oct 2018 10:29:06 +0800
In-Reply-To: <7040427b-f580-ec33-8afa-35dcf5735abb@gmail.com>
References: <1538212903-14331-1-git-send-email-houlong.wei@mediatek.com>
         <1538212903-14331-3-git-send-email-houlong.wei@mediatek.com>
         <7040427b-f580-ec33-8afa-35dcf5735abb@gmail.com>
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On Sat, 2018-09-29 at 20:50 +0800, Matthias Brugger wrote:
> 
> On 29/09/2018 11:21, Houlong Wei wrote:
> [...]
> 
> > +static int cmdq_pkt_append_command(struct cmdq_pkt *pkt, enum cmdq_code code,
> > +				   u32 arg_a, u32 arg_b)
> > +{
> > +	u64 *cmd_ptr;
> > +
> > +	if (unlikely(pkt->cmd_buf_size + CMDQ_INST_SIZE > pkt->buf_size)) {
> > +		pkt->cmd_buf_size += CMDQ_INST_SIZE;
> 
> Can you plesae provide some example code of a driver that will use this API, I
> still don't understand why you need to update the cmd_buf_size here.

In our previous design, when appending a new command to buffer and the
buffer gets overflow, we will re-allocate a larger buffer to use.
CK.Hu had concern about the performance of buffer re-allocation. Please
refer:
http://lists.infradead.org/pipermail/linux-mediatek/2018-June/013797.html
One of his suggestions is that the consumer dynamically allocates buffer
with a initial size. Because the consumer doesn't know how to calculate
the buffer size. So we increase cmdq_buf_size here, that will help the
consumer get the buffer size in developing phase. In release driver
code, consumer passes a constant value to function call
cmdq_pkt_create(client, cmdq_buffer_size), cmdq_buffer_size is the
specified command queue buffer size.

> 
> > +		WARN_ON(1);
> 
> can we add some debug information:
> WARN_ON(1, "%s: buffer size too small for the amount of commands", __func__);
> 
> Would it make sense to use WARN_ONCE()?
> 
Yes, I will add debug information and use WARN_ONCE().

> > +		return -ENOMEM;
> > +	}
> > +	cmd_ptr = pkt->va_base + pkt->cmd_buf_size;
> > +	(*cmd_ptr) = (u64)((code << CMDQ_OP_CODE_SHIFT) | arg_a) << 32 | arg_b;
> > +	pkt->cmd_buf_size += CMDQ_INST_SIZE;
> > +
> > +	return 0;
> > +}
> 
> Thanks,
> Matthias