linux-kernel - Re: [PATCH v20 2/4] mailbox: mediatek: Add Mediatek CMDQ driver

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Message-ID: <CABb+yY2dzcR4fYvrSQK5jemwUSkYVJ8aWEmiE6wstw-Yyqy7bw@mail.gmail.com>
Date:   Thu, 23 Feb 2017 09:40:43 +0530
From:   Jassi Brar <jassisinghbrar@...il.com>
To:     Horng-Shyang Liao <hs.liao@...iatek.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Daniel Kurtz <djkurtz@...omium.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Devicetree List <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.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>,
        CK HU <ck.hu@...iatek.com>,
        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>,
        Houlong Wei <houlong.wei@...iatek.com>
Subject: Re: [PATCH v20 2/4] mailbox: mediatek: Add Mediatek CMDQ driver

On Wed, Feb 22, 2017 at 8:42 AM, Horng-Shyang Liao <hs.liao@...iatek.com> wrote:
> On Thu, 2017-02-16 at 21:02 +0530, Jassi Brar wrote:
>> On Mon, Feb 6, 2017 at 11:07 AM, Horng-Shyang Liao <hs.liao@...iatek.com> wrote:
>> > Hi Jassi,
>> >
>> > On Wed, 2017-02-01 at 10:52 +0530, Jassi Brar wrote:
>> >> On Thu, Jan 26, 2017 at 2:07 PM, Horng-Shyang Liao <hs.liao@...iatek.com> wrote:
>> >> > Hi Jassi,
>> >> >
>> >> > On Thu, 2017-01-26 at 10:08 +0530, Jassi Brar wrote:
>> >> >> On Wed, Jan 4, 2017 at 8:36 AM, HS Liao <hs.liao@...iatek.com> wrote:
>> >> >>
>> >> >> > diff --git a/drivers/mailbox/mtk-cmdq-mailbox.c b/drivers/mailbox/mtk-cmdq-mailbox.c
>> >> >> > new file mode 100644
>> >> >> > index 0000000..747bcd3
>> >> >> > --- /dev/null
>> >> >> > +++ b/drivers/mailbox/mtk-cmdq-mailbox.c
>> >> >>
>> >> >> ...
>> >> >>
>> >> >> > +static void cmdq_task_exec(struct cmdq_pkt *pkt, struct cmdq_thread *thread)
>> >> >> > +{
>> >> >> > +       struct cmdq *cmdq;
>> >> >> > +       struct cmdq_task *task;
>> >> >> > +       unsigned long curr_pa, end_pa;
>> >> >> > +
>> >> >> > +       cmdq = dev_get_drvdata(thread->chan->mbox->dev);
>> >> >> > +
>> >> >> > +       /* Client should not flush new tasks if suspended. */
>> >> >> > +       WARN_ON(cmdq->suspended);
>> >> >> > +
>> >> >> > +       task = kzalloc(sizeof(*task), GFP_ATOMIC);
>> >> >> > +       task->cmdq = cmdq;
>> >> >> > +       INIT_LIST_HEAD(&task->list_entry);
>> >> >> > +       task->pa_base = dma_map_single(cmdq->mbox.dev, pkt->va_base,
>> >> >> > +                                      pkt->cmd_buf_size, DMA_TO_DEVICE);
>> >> >> >
>> >> >> You seem to parse the requests and responses, that should ideally be
>> >> >> done in client driver.
>> >> >> Also, we are here in atomic context, can you move it in client driver
>> >> >> (before the spin_lock)?
>> >> >> Maybe by adding a new 'pa_base' member as well in 'cmdq_pkt'.
>> >> >
>> >> > will do
>> >
>> > I agree with moving dma_map_single out from spin_lock.
>> >
>> > However, mailbox clients cannot map virtual memory to mailbox
>> > controller's device for DMA.
>> >
>> If DMA is a resource used by MBox to transfer data, then yes the
>> mapping needs to be done in the Mbox controller driver. To map memory
>> outside of spinlock, you could schedule a tasklet in send_data() ?
>
> Hi Jassi,
>
> For CMDQ, the order of CMDQ tasks should be guaranteed.
> However, it seems tasklet cannot ensure this requirement.
>
> Quote from Linux Device Drivers 3rd edition ch7.
> "void tasklet_schedule(struct tasklet_struct *t);
>   Schedule the tasklet for execution. If a tasklet is scheduled again
> before it has a chance to run, it runs only once...."
>
Not sure what bothers you.
If you only add requests to a list, protected by some spinlock, during
send_datam you could always iterate over (submit) requests in the
order you queued them.