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From:   Chun-Kuang Hu <chunkuang.hu@kernel.org>
Date:   Fri, 24 Jul 2020 23:55:33 +0800
Message-ID: <CAAOTY__KYH4G3E+c=zoOk==hPJHsAd5u4Q0oj4adKstaoOciMg@mail.gmail.com>
Subject: Re: [PATCH v3 2/2] soc: mediatek: add mtk-devapc driver
To:     Neal Liu <neal.liu@mediatek.com>
Cc:     Chun-Kuang Hu <chunkuang.hu@kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        wsd_upstream <wsd_upstream@mediatek.com>,
        lkml <linux-kernel@vger.kernel.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@lists.infradead.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>
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Hi, Neal:

Neal Liu <neal.liu@mediatek.com> =E6=96=BC 2020=E5=B9=B47=E6=9C=8824=E6=97=
=A5 =E9=80=B1=E4=BA=94 =E4=B8=8B=E5=8D=882:55=E5=AF=AB=E9=81=93=EF=BC=9A
>
> Hi Chun-Kuang,
>
> On Fri, 2020-07-24 at 00:32 +0800, Chun-Kuang Hu wrote:
> > Hi, Neal:
> >
> > Neal Liu <neal.liu@mediatek.com> =E6=96=BC 2020=E5=B9=B47=E6=9C=8823=E6=
=97=A5 =E9=80=B1=E5=9B=9B =E4=B8=8B=E5=8D=882:11=E5=AF=AB=E9=81=93=EF=BC=9A
> > >
> > > Hi Chun-Kuang,
> > >
> > > On Wed, 2020-07-22 at 22:25 +0800, Chun-Kuang Hu wrote:
> > > > Hi, Neal:
> > > >
> > > > Neal Liu <neal.liu@mediatek.com> =E6=96=BC 2020=E5=B9=B47=E6=9C=882=
2=E6=97=A5 =E9=80=B1=E4=B8=89 =E4=B8=8A=E5=8D=8811:49=E5=AF=AB=E9=81=93=EF=
=BC=9A
> > > > >
> > > > > Hi Chun-Kuang,
> > > > >
> > > > > On Wed, 2020-07-22 at 07:21 +0800, Chun-Kuang Hu wrote:
> > > > > > Hi, Neal:
> > > > > >
> > > > > > Neal Liu <neal.liu@mediatek.com> =E6=96=BC 2020=E5=B9=B47=E6=9C=
=8821=E6=97=A5 =E9=80=B1=E4=BA=8C =E4=B8=8B=E5=8D=8812:00=E5=AF=AB=E9=81=93=
=EF=BC=9A
> > > > > > >
> > > > > >
> > > > > > > +
> > > > > > > +/*
> > > > > > > + * mtk_devapc_dump_vio_dbg - get the violation index and dum=
p the full violation
> > > > > > > + *                           debug information.
> > > > > > > + */
> > > > > > > +static bool mtk_devapc_dump_vio_dbg(struct mtk_devapc_contex=
t *ctx, u32 vio_idx)
> > > > > > > +{
> > > > > > > +       u32 shift_bit;
> > > > > > > +
> > > > > > > +       if (check_vio_mask(ctx, vio_idx))
> > > > > > > +               return false;
> > > > > > > +
> > > > > > > +       if (!check_vio_status(ctx, vio_idx))
> > > > > > > +               return false;
> > > > > > > +
> > > > > > > +       shift_bit =3D get_shift_group(ctx, vio_idx);
> > > > > > > +
> > > > > > > +       if (sync_vio_dbg(ctx, shift_bit))
> > > > > > > +               return false;
> > > > > > > +
> > > > > > > +       devapc_extract_vio_dbg(ctx);
> > > > > >
> > > > > > I think get_shift_group(), sync_vio_dbg(), and
> > > > > > devapc_extract_vio_dbg() should be moved out of vio_idx for-loo=
p (the
> > > > > > loop in devapc_violation_irq()) because these three function is=
 not
> > > > > > related to vio_idx.
> > > > > > Another question: when multiple vio_idx violation occur, vio_ad=
dr is
> > > > > > related to which one vio_idx? The latest happened one?
> > > > > >
> > > > >
> > > > > Actually, it's related to vio_idx. But we don't use it directly o=
n these
> > > > > function. I think below snip code might be better way to understa=
nd it.
> > > > >
> > > > > for (...)
> > > > > {
> > > > >         check_vio_mask()
> > > > >         check_vio_status()
> > > > >
> > > > >         // if get vio_idx, mask it temporarily
> > > > >         mask_module_irq(true)
> > > > >         clear_vio_status()
> > > > >
> > > > >         // dump violation info
> > > > >         get_shift_group()
> > > > >         sync_vio_dbg()
> > > > >         devapc_extract_vio_dbg()
> > > > >
> > > > >         // unmask
> > > > >         mask_module_irq(false)
> > > > > }
> > > >
> > > > This snip code does not explain any thing. I could rewrite this cod=
e as:
> > > >
> > > > for (...)
> > > > {
> > > >     check_vio_mask()
> > > >     check_vio_status()
> > > >
> > > >     // if get vio_idx, mask it temporarily
> > > >     mask_module_irq(true)
> > > >     clear_vio_status()
> > > >     // unmask
> > > >     mask_module_irq(false)
> > > > }
> > > >
> > > > // dump violation info
> > > > get_shift_group()
> > > > sync_vio_dbg()
> > > > devapc_extract_vio_dbg()
> > > >
> > > > And my version is identical with your version, isn't it?
> > >
> > > Sorry, I did not explain it clearly. Let's me try again.
> > > The reason why I put "dump violation info" between mask & unmask cont=
ext
> > > is because it has to stop interrupt first before dump violation info,
> > > and then unmask it to prepare next violation.
> > > These sequence guarantee that if multiple violation is triggered, we
> > > still have information to debug.
> > > If the code sequence in your version and multiple violation is
> > > triggered, there might be no any information but keeps entering ISR.
> > > Finally, system might be abnormal and watchdog timeout.
> > > In this case, we still don't have any information to debug.
> >
> > I still don't understand why no information to debug. For example when
> > vio_idx 5, 10, 15 has violation,
> > You would mask vio_idx 5 to get information, but vio_idx 10, 15 does
> > not mask yet.
> > In your words, when vio_idx 10, 15 not mask, you would not get any
> > debug information when you process vio_idx 5.
> >
> > In my version, I would clear all status, why keeps entering ISR?
>
> Think about this case, if someone tries to dump "AAA" module's register.
> It would keep read reg base, base+0x4, base+0x8, ...
> All these registers are in the same slave, which would be same vio_idx.
> (Take vio_idx 5 as example)
> In this case, vio_idx 5 will keep triggering interrupt. If you did not
> do "dump violation info" between mask & unmask, you cannot get any
> violation info until the last interrupt being handled.
> Normally, system will crash before last interrupt coming.

You have said that first vio_addr would be kept until it's 'handled'.
So the first vio_addr reg_base would be kept even though other
violation happen. And I could handle (clear status and dump info) it
then vio_addr would next violation's address. I'm confused with your
statement. If AAA is dumping register of vio_idx 5, BBB is dumping
register of vio_idx 10, CCC is dumping register of vio_idx 15, I think
you should mask all vio_idx not only one. So the code would be

for all vio_idx {
    mask_module_irq(true)
}

devapc_extract_vio_dbg()

for all vio_idx {
    clear_vio_status()
    mask_module_irq(false)
}

>
> >
> > >
> > > >
> > > > >
> > > > > About your question, vio_addr would be the first one.
> > > >
> > > > So other vio_addr would be dropped? Or hardware would keep all
> > > > vio_addr and you have some way to get all vio_addr?
> > > >
> > >
> > > In this case, hardware will drop other violation info and keep the fi=
rst
> > > one until it been handled.
> >
> > Does 'handled' mean status is cleared?
>
> "handled" means clear status and dump violation info.
>
> >
> > Regards,
> > Chun-Kuang.
> >
> > >
> > > > >
> > > > > > > +
> > > > > > > +       return true;
> > > > > > > +}
> > > > > > > +
> > > > > > > +/*
> > > > > > > + * devapc_violation_irq - the devapc Interrupt Service Routi=
ne (ISR) will dump
> > > > > > > + *                        violation information including wh=
ich master violates
> > > > > > > + *                        access slave.
> > > > > > > + */
> > > > > > > +static irqreturn_t devapc_violation_irq(int irq_number,
> > > > > > > +                                       struct mtk_devapc_con=
text *ctx)
> > > > > > > +{
> > > > > > > +       u32 vio_idx;
> > > > > > > +
> > > > > > > +       for (vio_idx =3D 0; vio_idx < ctx->vio_idx_num; vio_i=
dx++) {
> > > > > > > +               if (!mtk_devapc_dump_vio_dbg(ctx, vio_idx))
> > > > > > > +                       continue;
> > > > > > > +
> > > > > > > +               /* Ensure that violation info are written bef=
ore
> > > > > > > +                * further operations
> > > > > > > +                */
> > > > > > > +               smp_mb();
> > > > > > > +
> > > > > > > +               /*
> > > > > > > +                * Mask slave's irq before clearing vio statu=
s.
> > > > > > > +                * Must do it to avoid nested interrupt and p=
revent
> > > > > > > +                * unexpected behavior.
> > > > > > > +                */
> > > > > > > +               mask_module_irq(ctx, vio_idx, true);
> > > > > > > +
> > > > > > > +               clear_vio_status(ctx, vio_idx);
> > > > > > > +
> > > > > > > +               mask_module_irq(ctx, vio_idx, false);
> > > > > > > +       }
> > > > > > > +
> > > > > > > +       return IRQ_HANDLED;
> > > > > > > +}
> > > > > > > +
> > > > > > > +/*
>