Linux-ARM-Kernel Archive on lore.kernel.org
 help / color / Atom feed
From: Samuel Holland <samuel@sholland.org>
To: Jassi Brar <jassisinghbrar@gmail.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Ondrej Jirman <megous@megous.com>,
	Devicetree List <devicetree@vger.kernel.org>,
	linux-sunxi@googlegroups.com,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Maxime Ripard <mripard@kernel.org>, Chen-Yu Tsai <wens@csie.org>,
	Rob Herring <robh+dt@kernel.org>,
	Philipp Zabel <p.zabel@pengutronix.de>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v6 2/6] mailbox: sun6i-msgbox: Add a new mailbox driver
Date: Fri, 14 Feb 2020 21:48:47 -0600
Message-ID: <89168ba0-a8ac-b433-3f93-412b22a9bc1a@sholland.org> (raw)
In-Reply-To: <72dc2074-c06d-4bdf-ca5f-b4007f492407@sholland.org>

On 2/12/20 8:18 PM, Samuel Holland wrote:
> Jassi,
> 
> On 2/12/20 8:02 PM, Jassi Brar wrote:
>> On Sun, Jan 12, 2020 at 11:18 PM Samuel Holland <samuel@sholland.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?

After more thought, I would prefer to keep the check. It is fast/simple, and it
keeps the hardware from getting into an inconsistent state. Silently dropping
messages sounds like a poor quality of implementation.

send_data() is documented in mailbox_controller.h as returning EBUSY, and I see
multiple other mailbox controllers implementing the same or a similar check. If
that is not the way you intend for the API to work, then please update the
comments in mailbox_controller.h.

Thanks,
Samuel

>> .....
>>> +
>>> +       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
> 


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply index

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-13  5:18 [PATCH v6 0/6] Allwinner sun6i message box support Samuel Holland
2020-01-13  5:18 ` [PATCH v6 1/6] dt-bindings: mailbox: Add a sun6i message box binding Samuel Holland
2020-01-13  9:30   ` Maxime Ripard
2020-01-13 22:38   ` Rob Herring
2020-01-13  5:18 ` [PATCH v6 2/6] mailbox: sun6i-msgbox: Add a new mailbox driver Samuel Holland
2020-01-13  9:15   ` Philipp Zabel
2020-02-13  2:02   ` Jassi Brar
2020-02-13  2:18     ` Samuel Holland
2020-02-15  3:48       ` Samuel Holland [this message]
2020-02-15  4:47         ` Jassi Brar
2020-02-15  6:19           ` [PATCH] mailbox: sun6i-msgbox: Remove unneeded FIFO status check Samuel Holland
2020-01-13  5:18 ` [PATCH v6 3/6] ARM: dts: sunxi: a83t: Add msgbox node Samuel Holland
2020-01-13  5:18 ` [PATCH v6 4/6] ARM: dts: sunxi: h3/h5: " Samuel Holland
2020-01-13  5:18 ` [PATCH v6 5/6] arm64: dts: allwinner: a64: " Samuel Holland
2020-01-13  5:18 ` [PATCH v6 6/6] arm64: dts: allwinner: h6: " Samuel Holland
2020-02-13  1:43 ` [PATCH v6 0/6] Allwinner sun6i message box support Samuel Holland

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=89168ba0-a8ac-b433-3f93-412b22a9bc1a@sholland.org \
    --to=samuel@sholland.org \
    --cc=devicetree@vger.kernel.org \
    --cc=jassisinghbrar@gmail.com \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-sunxi@googlegroups.com \
    --cc=mark.rutland@arm.com \
    --cc=megous@megous.com \
    --cc=mripard@kernel.org \
    --cc=p.zabel@pengutronix.de \
    --cc=robh+dt@kernel.org \
    --cc=wens@csie.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-ARM-Kernel Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-arm-kernel/0 linux-arm-kernel/git/0.git
	git clone --mirror https://lore.kernel.org/linux-arm-kernel/1 linux-arm-kernel/git/1.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-arm-kernel linux-arm-kernel/ https://lore.kernel.org/linux-arm-kernel \
		linux-arm-kernel@lists.infradead.org
	public-inbox-index linux-arm-kernel

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.infradead.lists.linux-arm-kernel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git