netdev - Re: [PATCH v4 02/17] octeontx2-pf: Mailbox communication with AF

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Message-ID: <CA+sq2Ce7nFbPu33Cu5YwgfEdfjOSWQwA1nijjtF7KKBYSph1TQ@mail.gmail.com>
Date:   Thu, 23 Jan 2020 00:57:22 +0530
From:   Sunil Kovvuri <sunil.kovvuri@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Linux Netdev List <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Michal Kubecek <mkubecek@...e.cz>,
        Sunil Goutham <sgoutham@...vell.com>,
        Geetha sowjanya <gakula@...vell.com>,
        Christina Jacob <cjacob@...vell.com>,
        Subbaraya Sundeep <sbhatta@...vell.com>,
        Aleksey Makarov <amakarov@...vell.com>
Subject: Re: [PATCH v4 02/17] octeontx2-pf: Mailbox communication with AF

On Tue, Jan 21, 2020 at 9:30 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Tue, 21 Jan 2020 18:51:36 +0530, sunil.kovvuri@...il.com wrote:
> > From: Sunil Goutham <sgoutham@...vell.com>
> >
> > In the resource virtualization unit (RVU) each of the PF and AF
> > (admin function) share a 64KB of reserved memory region for
> > communication. This patch initializes PF <=> AF mailbox IRQs,
> > registers handlers for processing these communication messages.
> > Also adds support to process these messages in both directions
> > ie responses to PF initiated DOWN (PF => AF) messages and AF
> > initiated UP messages (AF => PF).
> >
> > Mbox communication APIs and message formats are defined in AF driver
> > (drivers/net/ethernet/marvell/octeontx2/af), mbox.h from AF driver is
> > included here to avoid duplication.
> >
> > Signed-off-by: Geetha sowjanya <gakula@...vell.com>
> > Signed-off-by: Christina Jacob <cjacob@...vell.com>
> > Signed-off-by: Subbaraya Sundeep <sbhatta@...vell.com>
> > Signed-off-by: Aleksey Makarov <amakarov@...vell.com>
> > Signed-off-by: Sunil Goutham <sgoutham@...vell.com>
>
> >
> >  struct otx2_hw {
> > +
> > +     /* MSI-X*/
>                 ^
>
> The white space here is fairly loose
>

Will fix the white space issues.

> > +static inline void otx2_sync_mbox_bbuf(struct otx2_mbox *mbox, int devid)
> > +{
> > +     u16 msgs_offset = ALIGN(sizeof(struct mbox_hdr), MBOX_MSG_ALIGN);
> > +     void *hw_mbase = mbox->hwbase + (devid * MBOX_SIZE);
> > +     struct otx2_mbox_dev *mdev = &mbox->dev[devid];
> > +     struct mbox_hdr *hdr;
> > +     u64 msg_size;
> > +
> > +     if (mdev->mbase == hw_mbase)
> > +             return;
> > +
> > +     hdr = hw_mbase + mbox->rx_start;
> > +     msg_size = hdr->msg_size;
> > +
> > +     if (msg_size > mbox->rx_size - msgs_offset)
> > +             msg_size = mbox->rx_size - msgs_offset;
> > +
> > +     /* Copy mbox messages from mbox memory to bounce buffer */
> > +     memcpy(mdev->mbase + mbox->rx_start,
> > +            hw_mbase + mbox->rx_start, msg_size + msgs_offset);
>
> I'm slightly concerned about the use of non-iomem helpers like memset
> and memcpy on what I understand to be IOMEM, and the lack of memory
> barriers. But then again, I don't know much about iomem_wc(), is this
> code definitely correct from memory ordering perspective?
> (The memory barrier in otx2_mbox_msg_send() should probably be just
> wmb(), syncing with HW is unrelated with SMP.)

The mailbox region is a normal memory which is exposed to two devices
via PCI BARs.
And the writeq() call (to trigger IRQ) inside otx2_mbox_msg_send() has a wmb().

Thanks,
Sunil.