linux-kernel - Re: [PATCH v3 2/2] soc: mediatek: add mtk-devapc driver

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Message-ID: <1595573719.24412.9.camel@mtkswgap22>
Date:   Fri, 24 Jul 2020 14:55:19 +0800
From:   Neal Liu <neal.liu@...iatek.com>
To:     Chun-Kuang Hu <chunkuang.hu@...nel.org>
CC:     Neal Liu <neal.liu@...iatek.com>, Rob Herring <robh+dt@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        wsd_upstream <wsd_upstream@...iatek.com>,
        lkml <linux-kernel@...r.kernel.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3 2/2] soc: mediatek: add mtk-devapc driver

Hi Chun-Kuang,

On Fri, 2020-07-24 at 00:32 +0800, Chun-Kuang Hu wrote:
> Hi, Neal:
> 
> Neal Liu <neal.liu@...iatek.com> 於 2020年7月23日 週四 下午2:11寫道：
> >
> > Hi Chun-Kuang,
> >
> > On Wed, 2020-07-22 at 22:25 +0800, Chun-Kuang Hu wrote:
> > > Hi, Neal:
> > >
> > > Neal Liu <neal.liu@...iatek.com> 於 2020年7月22日 週三 上午11:49寫道：
> > > >
> > > > Hi Chun-Kuang,
> > > >
> > > > On Wed, 2020-07-22 at 07:21 +0800, Chun-Kuang Hu wrote:
> > > > > Hi, Neal:
> > > > >
> > > > > Neal Liu <neal.liu@...iatek.com> 於 2020年7月21日 週二 下午12:00寫道：
> > > > > >
> > > > >
> > > > > > +
> > > > > > +/*
> > > > > > + * mtk_devapc_dump_vio_dbg - get the violation index and dump the full violation
> > > > > > + *                           debug information.
> > > > > > + */
> > > > > > +static bool mtk_devapc_dump_vio_dbg(struct mtk_devapc_context *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 = 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-loop (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_addr 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 on these
> > > > function. I think below snip code might be better way to understand 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 code 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 context
> > 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.

> 
> >
> > >
> > > >
> > > > 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 first
> > 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 Routine (ISR) will dump
> > > > > > + *                        violation information including which master violates
> > > > > > + *                        access slave.
> > > > > > + */
> > > > > > +static irqreturn_t devapc_violation_irq(int irq_number,
> > > > > > +                                       struct mtk_devapc_context *ctx)
> > > > > > +{
> > > > > > +       u32 vio_idx;
> > > > > > +
> > > > > > +       for (vio_idx = 0; vio_idx < ctx->vio_idx_num; vio_idx++) {
> > > > > > +               if (!mtk_devapc_dump_vio_dbg(ctx, vio_idx))
> > > > > > +                       continue;
> > > > > > +
> > > > > > +               /* Ensure that violation info are written before
> > > > > > +                * further operations
> > > > > > +                */
> > > > > > +               smp_mb();
> > > > > > +
> > > > > > +               /*
> > > > > > +                * Mask slave's irq before clearing vio status.
> > > > > > +                * Must do it to avoid nested interrupt and prevent
> > > > > > +                * 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;
> > > > > > +}
> > > > > > +
> > > > > > +/*