linux-kernel - Re: [PATCH v6 2/6] mailbox: sun6i-msgbox: Add a new mailbox driver

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Date:   Wed, 12 Feb 2020 20:18:42 -0600
From:   Samuel Holland <samuel@...lland.org>
To:     Jassi Brar <jassisinghbrar@...il.com>
Cc:     Maxime Ripard <mripard@...nel.org>, Chen-Yu Tsai <wens@...e.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Ondrej Jirman <megous@...ous.com>,
        Vasily Khoruzhick <anarsoul@...il.com>,
        Devicetree List <devicetree@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-sunxi@...glegroups.com
Subject: Re: [PATCH v6 2/6] mailbox: sun6i-msgbox: Add a new mailbox driver

Jassi,

On 2/12/20 8:02 PM, Jassi Brar wrote:
> On Sun, Jan 12, 2020 at 11:18 PM Samuel Holland <samuel@...lland.org> wrote:
>>
>> +static int sun6i_msgbox_send_data(struct mbox_chan *chan, void *data)
>> +{
>> +       struct sun6i_msgbox *mbox = to_sun6i_msgbox(chan);
>> +       int n = channel_number(chan);
>> +       uint32_t msg = *(uint32_t *)data;
>> +
>> +       /* Using a channel backwards gets the hardware into a bad state. */
>> +       if (WARN_ON_ONCE(!(readl(mbox->regs + CTRL_REG(n)) & CTRL_TX(n))))
>> +               return 0;
>> +
>> +       /* We cannot post a new message if the FIFO is full. */
>> +       if (readl(mbox->regs + FIFO_STAT_REG(n)) & FIFO_STAT_MASK) {
>> +               mbox_dbg(mbox, "Channel %d busy sending 0x%08x\n", n, msg);
>> +               return -EBUSY;
>> +       }
>> +
> This check should go into sun6i_msgbox_last_tx_done().
> send_data() assumes all is clear to send next packet.

sun6i_msgbox_last_tx_done() already checks that the FIFO is completely empty (as
the big comment explains). So this error could only be hit in the knows_txdone
== true case, if the client pipelines multiple messages by calling
mbox_client_txdone() before the message is actually removed from the FIFO.

>From the comments in mailbox_controller.h, this kind of usage looks to be
unsupported. In that case, I could remove the check entirely. Does that sound right?

> .....
>> +
>> +       mbox->controller.dev           = dev;
>> +       mbox->controller.ops           = &sun6i_msgbox_chan_ops;
>> +       mbox->controller.chans         = chans;
>> +       mbox->controller.num_chans     = NUM_CHANS;
>> +       mbox->controller.txdone_irq    = false;
>> +       mbox->controller.txdone_poll   = true;
>> +       mbox->controller.txpoll_period = 5;
>> +
> nit:  just a single space should do too.
> 
> Sorry, for some reason I thought I had replied to this patch, but
> apparently not. My mistake. Do you want to revise this submission or
> send another patch on top?

For just this change, it would be simpler to send a follow-up patch.

> thanks

Thank you,
Samuel