linux-kernel - Re: [PATCH v2 2/2] soc: mediatek: add mtk-devapc driver

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Date:   Fri, 10 Jul 2020 11:23:43 +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>,
        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 v2 2/2] soc: mediatek: add mtk-devapc driver

Hi Chun-Kuang,

Thanks for your review.

On Thu, 2020-07-09 at 21:01 +0800, Chun-Kuang Hu wrote:
> Hi, Neal:
> 
> Neal Liu <neal.liu@...iatek.com> 於 2020年7月9日 週四 下午5:13寫道：
> >
> > MediaTek bus fabric provides TrustZone security support and data
> > protection to prevent slaves from being accessed by unexpected
> > masters.
> > The security violation is logged and sent to the processor for
> > further analysis or countermeasures.
> >
> > Any occurrence of security violation would raise an interrupt, and
> > it will be handled by mtk-devapc driver. The violation
> > information is printed in order to find the murderer.
> >
> > Signed-off-by: Neal Liu <neal.liu@...iatek.com>
> 
> [snip]
> 
> > +
> > +static u32 get_shift_group(struct mtk_devapc_context *devapc_ctx,
> > +                          int slave_type, int vio_idx)
> 
> vio_idx  is useless, so remove it.
> 

yes, my mistake. I'll remove it on next patch.

> > +{
> > +       u32 vio_shift_sta;
> > +       void __iomem *reg;
> > +       int bit;
> > +
> > +       reg = mtk_devapc_pd_get(devapc_ctx, slave_type, VIO_SHIFT_STA, 0);
> > +       vio_shift_sta = readl(reg);
> > +
> > +       for (bit = 0; bit < 32; bit++) {
> > +               if ((vio_shift_sta >> bit) & 0x1)
> > +                       break;
> > +       }
> > +
> > +       return bit;
> > +}
> > +
> 
> [snip]
> 
> > +
> > +/*
> > + * 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 *devapc_ctx)
> > +{
> > +       const struct mtk_device_info **device_info;
> > +       int slave_type_num;
> > +       int vio_idx = -1;
> > +       int slave_type;
> > +
> > +       slave_type_num = devapc_ctx->slave_type_num;
> > +       device_info = devapc_ctx->device_info;
> > +
> > +       for (slave_type = 0; slave_type < slave_type_num; slave_type++) {
> 
> If slave_type_num is 1, I think the code should be simpler.

slave_type_num is depends on DT data, it's not always 1.

> 
> > +               if (!mtk_devapc_dump_vio_dbg(devapc_ctx, slave_type, &vio_idx))
> > +                       continue;
> > +
> > +               /* Ensure that violation info are written before
> > +                * further operations
> > +                */
> > +               smp_mb();
> > +
> > +               mask_module_irq(devapc_ctx, slave_type, vio_idx, true);
> 
> Why do you mask irq?

It has to mask slave's irq before clear violation status.
It's one of hardware design.

> 
> > +
> > +               clear_vio_status(devapc_ctx, slave_type, vio_idx);
> > +
> > +               mask_module_irq(devapc_ctx, slave_type, vio_idx, false);
> > +       }
> > +
> > +       return IRQ_HANDLED;
> > +}
> > +
> > +/*
> > + * start_devapc - initialize devapc status and start receiving interrupt
> > + *               while devapc violation is triggered.
> > + */
> 
> [snip]
> 
> > +
> > +struct mtk_device_info {
> > +       int sys_index;
> 
> Useless, so remove it.

We need to print it as our debug information.
But I did not apply it on this patch, I'll add it on next patch.

> 
> > +       int ctrl_index;
> 
> Ditto.
> 
> Regards,
> Chun-Kuang.
> 
> > +       int vio_index;
> > +};
> > +