linux-kernel - Re: [PATCH net-next v2 3/6] net: lan966x: add port module support

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Message-ID: <20211125092638.7b2u75zdv2ulekmo@soft-dev3-1.localhost>
Date:   Thu, 25 Nov 2021 10:26:38 +0100
From:   Horatiu Vultur <horatiu.vultur@...rochip.com>
To:     Andrew Lunn <andrew@...n.ch>
CC:     <davem@...emloft.net>, <kuba@...nel.org>, <robh+dt@...nel.org>,
        <UNGLinuxDriver@...rochip.com>, <p.zabel@...gutronix.de>,
        <linux@...linux.org.uk>, <netdev@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next v2 3/6] net: lan966x: add port module support

The 11/24/2021 18:59, Andrew Lunn wrote:

Hi Andrew,

> 
> > +static void lan966x_ifh_inject(u32 *ifh, size_t val, size_t pos, size_t length)
> > +{
> > +     int i;
> > +
> > +     for (i = pos; i < pos + length; ++i) {
> > +             if (val & BIT(i - pos))
> > +                     ifh[IFH_LEN - i / 32 - 1] |= BIT(i % 32);
> > +             else
> > +                     ifh[IFH_LEN - i / 32 - 1] &= ~(BIT(i % 32));
> > +     }
> > +}
> > +
> > +static void lan966x_gen_ifh(u32 *ifh, struct lan966x_frame_info *info,
> > +                         struct lan966x *lan966x)
> > +{
> > +     lan966x_ifh_inject(ifh, 1, IFH_POS_BYPASS, 1);
> > +     lan966x_ifh_inject(ifh, info->port, IFH_POS_DSTS, IFH_WID_DSTS);
> > +     lan966x_ifh_inject(ifh, info->qos_class, IFH_POS_QOS_CLASS,
> > +                        IFH_WID_QOS_CLASS);
> > +     lan966x_ifh_inject(ifh, info->ipv, IFH_POS_IPV, IFH_WID_IPV);
> > +}
> > +
> 
> > +     /* Write IFH header */
> > +     for (i = 0; i < IFH_LEN; ++i) {
> > +             /* Wait until the fifo is ready */
> > +             while (!(QS_INJ_STATUS_FIFO_RDY_GET(lan_rd(lan966x, QS_INJ_STATUS)) &
> > +                      BIT(grp)))
> > +                     ;
> > +
> > +             lan_wr((__force u32)cpu_to_be32(ifh[i]), lan966x,
> > +                    QS_INJ_WR(grp));
> 
> There is a lot of magic going on here constructing the IFH. Is it
> possible to define the structure using bit fields and __be32. You
> should then be able to skip this cpu_to_be32 and the ugly cast. And
> the actual structure should be a lot clearer.

If I undestood you correctly I have tried to do the following:

struct lan966x_ifh {
    __be32 timestamp;
    __be32 bypass : 1;
    __be32 port : 3;
    ...
};

But then I start to get errors from sparse:

error: invalid bitfield specifier for type restricted __be32.

On thing that I can do is to use packing() instead of
lan966x_ifh_inject() and declare ifh as __be32.
I think this will also work and simplify a little bit the code.

> 
> > +static int lan966x_rx_frame_word(struct lan966x *lan966x, u8 grp, bool ifh,
> > +                              u32 *rval)
> > +{
> > +     u32 bytes_valid;
> > +     u32 val;
> > +
> > +     val = lan_rd(lan966x, QS_XTR_RD(grp));
> > +     if (val == XTR_NOT_READY) {
> > +             if (ifh)
> > +                     return -EIO;
> > +
> > +             do {
> > +                     val = lan_rd(lan966x, QS_XTR_RD(grp));
> > +             } while (val == XTR_NOT_READY);
> 
> I would add some sort of timeout here, just in case the hardware
> breaks. You have quite a few such loops, it would be better to make
> use of the helpers in linux/iopoll.h.

Yes, I will do that, I will also add sime timeout also for injection.

> 

-- 
/Horatiu