linux-kernel - Re: [PATCH v4 2/2] mailbox: sprd: Add Spreadtrum mailbox driver

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Message-ID: <CABb+yY244ZCOk5kDtOR0oEYajwUVbXoSZdNiid__UuYbU=yB-Q@mail.gmail.com>
Date:   Thu, 21 May 2020 22:48:37 -0500
From:   Jassi Brar <jassisinghbrar@...il.com>
To:     Baolin Wang <baolin.wang7@...il.com>
Cc:     Rob Herring <robh+dt@...nel.org>, Orson Zhai <orsonzhai@...il.com>,
        Chunyan Zhang <zhang.lyra@...il.com>,
        Devicetree List <devicetree@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 2/2] mailbox: sprd: Add Spreadtrum mailbox driver

On Thu, May 21, 2020 at 7:24 AM Baolin Wang <baolin.wang7@...il.com> wrote:
>
> Hi Jassi,
>
> On Wed, May 13, 2020 at 2:32 PM Baolin Wang <baolin.wang7@...il.com> wrote:
> >
> > On Wed, May 13, 2020 at 2:05 PM Jassi Brar <jassisinghbrar@...il.com> wrote:
> > >
> > > On Tue, May 12, 2020 at 11:14 PM Baolin Wang <baolin.wang7@...il.com> wrote:
> > > >
> > > > Hi Jassi,
> > > >
> > > > On Thu, May 7, 2020 at 11:23 AM Baolin Wang <baolin.wang7@...il.com> wrote:
> > > > >
> > > > > Hi Jassi,
> > > > >
> > > > > On Thu, May 7, 2020 at 7:25 AM Jassi Brar <jassisinghbrar@...il.com> wrote:
> > > > > >
> > > > > > On Wed, May 6, 2020 at 8:29 AM Baolin Wang <baolin.wang7@...il.com> wrote:
> > > > > > >
> > > > > > > Hi Jassi,
> > > > > > >
> > > > > > > On Tue, Apr 28, 2020 at 11:10 AM Baolin Wang <baolin.wang7@...il.com> wrote:
> > > > > > > >
> > > > > > > > From: Baolin Wang <baolin.wang@...soc.com>
> > > > > > > >
> > > > > > > > The Spreadtrum mailbox controller supports 8 channels to communicate
> > > > > > > > with MCUs, and it contains 2 different parts: inbox and outbox, which
> > > > > > > > are used to send and receive messages by IRQ mode.
> > > > > > > >
> > > > > > > > Signed-off-by: Baolin Wang <baolin.wang@...soc.com>
> > > > > > > > Signed-off-by: Baolin Wang <baolin.wang7@...il.com>
> > > > > > > > ---
> > > > > > > > Changes from v3:
> > > > > > > >  - Save the id in mbox_chan.con_priv and remove the 'sprd_mbox_chan'
> > > > > > > >
> > > > > > > > Changes from v2:
> > > > > > > >  - None.
> > > > > > > >
> > > > > > > > Changes from v1:
> > > > > > > >  - None
> > > > > > >
> > > > > > > Gentle ping, do you have any other comments? Thanks.
> > > > > > >
> > > > > > Yea, I am still not sure about the error returned in send_data().  It
> > > > > > will either never hit or there will be no easy recovery from it. The
> > > > > > api expects the driver to tell it the last-tx was done only when it
> > > > > > can send the next message. (There may be case like sending depend on
> > > > > > remote, which can't be ensured before hand).
> > > > >
> > > > > Actually this is an unusual case, suppose the remote target did not
> > > > > fetch the message as soon as possile, which will cause the FIFO
> > > > > overflow, so in this case we  can not send messages to the remote
> > > > > target any more, otherwise messages will be lost. Thus we can return
> > > > > errors to users to indicate that something wrong with the remote
> > > > > target need to be checked.
> > > > >
> > > > > So this validation in send_data() is mostly for debugging for this
> > > > > abnormal case and we will not trigger this issue if the remote target
> > > > > works well. So I think it is useful to keep this validation in
> > > > > send_data(). Thanks.
> > > >
> > > > Any comments? Thanks.
> > > >
> > > Same as my last post.
> >
> > I think I've explained the reason why we need add this validation in
> > my previous email, I am not sure how do you think? You still want to
> > remove this validation?
>
> Gentle ping.
>
> As I explained in previous email, this validation is for an unusual
> case, suppose the remote target did not fetch the message as soon as
> possile, which will cause the FIFO overflow, so in this case we  can
> not send messages to the remote
> target any more, otherwise messages will be lost. Thus we can return
> errors to users to indicate that something wrong with the remote
> target need to be checked.
>
> So this validation in send_data() is mostly for debugging for this
> abnormal case and we will not trigger this issue if the remote target
> works well. So I think it is useful to keep this validation in
> send_data(). What do you think? Thanks.
>
I still think the same as before.
You should do this check before you call mbox_chan_txdone() and wait
if busy ... which is exactly the purpose of txdone().
It seems harmless to be paranoid and place a block of code in
practically "if 0", but that sets bad precedence for other drivers. So
please move the check before txdone().

thanks.