linux-kernel - Re: [PATCH v23 4/4] soc: mediatek: Add Mediatek CMDQ helper

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Date:   Thu, 27 Sep 2018 18:30:46 +0800
From:   houlong wei <houlong.wei@...iatek.com>
To:     Matthias Brugger <matthias.bgg@...il.com>
CC:     Jassi Brar <jassisinghbrar@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Daniel Kurtz <djkurtz@...omium.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        srv_heupstream <srv_heupstream@...iatek.com>,
        Sascha Hauer <kernel@...gutronix.de>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        "Nicolas Boichat" <drinkcat@...omium.org>,
        CK Hu (胡俊光) 
        <ck.hu@...iatek.com>,
        "Bibby Hsieh (謝濟遠)" 
        <Bibby.Hsieh@...iatek.com>,
        YT Shen (沈岳霆) 
        <Yt.Shen@...iatek.com>,
        Daoyuan Huang (黃道原) 
        <Daoyuan.Huang@...iatek.com>,
        Jiaguang Zhang (张加广) 
        <Jiaguang.Zhang@...iatek.com>,
        Dennis-YC Hsieh (謝宇哲) 
        <Dennis-YC.Hsieh@...iatek.com>,
        Monica Wang (王孟婷) 
        <monica.wang@...iatek.com>,
        Hs Liao (廖宏祥) 
        <Hs.Liao@...iatek.com>,
        Ginny Chen (陳治傑) 
        <ginny.chen@...iatek.com>,
        Enzhu Wang (王恩柱) 
        <enzhu.wang@...iatek.com>, <houlong.wei@...iatek.com>
Subject: Re: [PATCH v23 4/4] soc: mediatek: Add Mediatek CMDQ helper

On Thu, 2018-09-27 at 15:50 +0800, Matthias Brugger wrote:
> 
> On 27/09/2018 03:57, 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;
> >>
> >> Why do we update the cmd_buf_size here?
> > 
> > Because in developing phase of consumer driver, the consumer has to know
> > the real command buffer size after adding command failure. Then the
> > consumer will increase the size and run the cmdq flow (cmdq_pkt_create,
> > cmdq_pkt_write/wfe...) again. Finally, the consumer get the real size
> > and fix it.
> > 
> 
> But the consumer should know the size it needs for it's buffer and if not it
> should be able to decide on it's own how much space it needs. If he get's a
> -ENOMEM he implicitly knows that he has to increase the buf_size. Now the size
> depends on how many command he has pending and wasn't able to write to the cmdq_pkt.
> 
> Regards,
> Matthias

The consumer doesn't know how to calculate the command buffer size that
he needs.
When the consumer driver is developing, he could ignore the return value
of cmdq_pkt_write and other command appending functions.
He can print the pkt->cmdq_buf_size after cmdq_pkt_flush() or
cmdq_pkt_flush_async() failure. Now he can get the buffer size he needs.

I copy your another comment here, so I can reply in one mail.
>>If we want to write out a warning to the kernel log, then we should
>>but that in the if (unlikely(pkt->cmd_buf_size + CMDQ_INST_SIZE
>>pkt->buf_size)) from cmdq_pkt_append_command to make it consistent
>>between cmdq_pkt_write, cmdq_pkt_write_mask and cmdq_pkt_finalize.

Thanks, I will move WARN_ON() into cmdq_pkt_append_command() before
returning -ENOMEM.

After your confirmation of the comments above, I will re-send a new
patch.