linux-kernel - Re: [PATCH] net: netsec: replace cpu_relax() with timeout handling for register checks

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Message-ID: <5027002.31r3eYUQgx@fedora>
Date:   Mon, 20 Nov 2023 11:19:48 +0900
From:   Ryosuke Saito <ryosuke.saito@...aro.org>
To:     Simon Horman <horms@...nel.org>
Cc:     jaswinder.singh@...aro.org, ilias.apalodimas@...aro.org,
        davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, masahisa.kojima@...aro.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: netsec: replace cpu_relax() with timeout handling for
 register checks

[Resend again after removing an HTML format. Sorry for that.]

Hi Simon-san,

On Mon, Nov 20, 2023 at 3:53 AM Simon Horman <horms@...nel.org> wrote:
>
> On Fri, Nov 17, 2023 at 05:10:02PM +0900, Ryosuke Saito wrote:
> > The cpu_relax() loops have the potential to hang if the specified
> > register bits are not met on condition. The patch replaces it with
> > usleep_range() and netsec_wait_while_busy() which includes timeout
> > logic.
> >
> > Additionally, if the error condition is met during interrupting DMA
> > transfer, there's no recovery mechanism available. In that case, any
> > frames being sent or received will be discarded, which leads to
> > potential frame loss as indicated in the comments.
> >
> > Signed-off-by: Ryosuke Saito <ryosuke.saito@...aro.org>
> > ---
> >  drivers/net/ethernet/socionext/netsec.c | 35 ++++++++++++++++---------
> >  1 file changed, 23 insertions(+), 12 deletions(-)
>
> ...
>
> > @@ -1476,9 +1483,13 @@ static int netsec_reset_hardware(struct netsec_priv 
*priv,
> >       netsec_write(priv, NETSEC_REG_DMA_MH_CTRL, MH_CTRL__MODE_TRANS);
> >       netsec_write(priv, NETSEC_REG_PKT_CTRL, value);
> >
> > -     while ((netsec_read(priv, NETSEC_REG_MODE_TRANS_COMP_STATUS) &
> > -             NETSEC_MODE_TRANS_COMP_IRQ_T2N) == 0)
> > -             cpu_relax();
> > +     usleep_range(100000, 120000);
> > +
> > +     if ((netsec_read(priv, NETSEC_REG_MODE_TRANS_COMP_STATUS) &
> > +                      NETSEC_MODE_TRANS_COMP_IRQ_T2N) == 0) {
> > +             dev_warn(priv->dev,
> > +                      "%s: trans comp timeout.\n", __func__);
> > +     }
>
> Hi Saito-san,
>
> could you add some colour to how the new code satisfies the
> requirements of the hardware?  In particular, the use of
> usleep_range(), and the values passed to it.


For the h/w requirements, I followed U-Boot upstream:
https://elixir.bootlin.com/u-boot/latest/source/drivers/net/sni_netsec.c

It has the same function as well, netsec_reset_hardware(), and the 
corresponding potion is the following read-check loop:

1012         value = 100;
1013         while ((netsec_read_reg(priv, NETSEC_REG_MODE_TRANS_COMP_STATUS) 
&
1014                 NETSEC_MODE_TRANS_COMP_IRQ_T2N) == 0) {
1015                 udelay(1000);
1016                 if (--value == 0) {
1017                         value = netsec_read_reg(priv, 
NETSEC_REG_MODE_TRANS_COMP_STATUS);
1018                         pr_err("%s:%d timeout! val=%x\n", __func__, 
__LINE__, value);
1019                         break;
1020                 }
1021         }

The maximum t/o = 1000us * 100 + read time

Regards,
Ryo