Re: [PATCH v4 2/2] soc: mediatek: add mtk-devapc driver

[Chun-Kuang Hu <chunkuang.hu@kernel.org>]

Hi, Neal:

Neal Liu <neal.liu@mediatek.com> 於 2020年8月3日 週一 上午11:32寫道：
>
> Hi Chun-Kuang,
>
> On Fri, 2020-07-31 at 23:03 +0800, Chun-Kuang Hu wrote:
> > Hi, Neal:
> >
> > Neal Liu <neal.liu@mediatek.com> 於 2020年7月31日 週五 上午10:44寫道：
> > >
> > > Hi Chun-Kuang,
> > >
> > >
> > > On Thu, 2020-07-30 at 00:38 +0800, Chun-Kuang Hu wrote:
> > > > Hi, Neal:
> > > >
> > > > Neal Liu <neal.liu@mediatek.com> 於 2020年7月29日 週三 下午4:29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@mediatek.com>
> > > > > ---
> > > >
> > > > [snip]
> > > >
> > > > > +
> > > > > +/*
> > > > > + * devapc_extract_vio_dbg - extract full violation information after doing
> > > > > + *                          shift mechanism.
> > > > > + */
> > > > > +static void devapc_extract_vio_dbg(struct mtk_devapc_context *ctx)
> > > > > +{
> > > > > +       const struct mtk_devapc_vio_dbgs *vio_dbgs;
> > > > > +       struct mtk_devapc_vio_info *vio_info;
> > > > > +       void __iomem *vio_dbg0_reg;
> > > > > +       void __iomem *vio_dbg1_reg;
> > > > > +       u32 dbg0;
> > > > > +
> > > > > +       vio_dbg0_reg = ctx->devapc_pd_base + ctx->offset->vio_dbg0;
> > > > > +       vio_dbg1_reg = ctx->devapc_pd_base + ctx->offset->vio_dbg1;
> > > > > +
> > > > > +       vio_dbgs = ctx->vio_dbgs;
> > > > > +       vio_info = ctx->vio_info;
> > > > > +
> > > > > +       /* Starts to extract violation information */
> > > > > +       dbg0 = readl(vio_dbg0_reg);
> > > > > +       vio_info->vio_addr = readl(vio_dbg1_reg);
> > > > > +
> > > > > +       vio_info->master_id = (dbg0 & vio_dbgs->mstid.mask) >>
> > > > > +                             vio_dbgs->mstid.start;
> > > >
> > > > What is master_id? How could we use it to debug? For example, if we
> > > > get a master_id = 1, what should we do for this?
> > > >
> > > > > +       vio_info->domain_id = (dbg0 & vio_dbgs->dmnid.mask) >>
> > > > > +                             vio_dbgs->dmnid.start;
> > > >
> > > > What is domain_id? How could we use it to debug? For example, if we
> > > > get a domain_id = 2, what should we do for this?
> > > >
> > >
> > > master_id and domain_id belongs our bus side-band signal info. It can
> > > help us to find the violation master.
> >
> > Does 'violation master' means the hardware could access the protected
> > register? (ex. CPU, GCE, ...) If so, I think it's better to add
> > comment to explain how to map (master_id, domain_id) to a hardware
> > (maybe the device in device tree) because every body does not know
> > what the number means. Don't try to translate the number to a string
> > because this would cost much time to do this. Just print a number and
> > we could find out the master by the comment.
>
> 'violation master' means the master which violates the permission
> control. For example, if we set permission 'Secure R/W only' as CPU to
> spi register. When violation is triggered, it means CPU access spi
> register through normal world instead of secure world, which is not
> allowed.
>
> 'master_id' cannot use the simple comments to describe which master it
> is. It depends on violation slaves. For example, if there are two
> violations:
> 1. CPU access spi reg
> 2. CPU access timer reg
> It might be different 'master_id' for CPU on these two cases.
> I would prefer to remain the id number if translate to a string is a bad
> idea.
> Thanks !

It seams that master_id and domain_id does not help for debug. When we
get master_id = 1 and domain_id = 2, we don't know what it mean. I
think we just need violation address because we could find the driver
that write this address and the bug would be inside this driver. So
need not to process master_id and domain_id.

Regards,
Chun-Kuang.

>
> >
> > >
> > > > > +       vio_info->write = ((dbg0 & vio_dbgs->vio_w.mask) >>
> > > > > +                           vio_dbgs->vio_w.start) == 1;
> > > > > +       vio_info->read = ((dbg0 & vio_dbgs->vio_r.mask) >>
> > > > > +                         vio_dbgs->vio_r.start) == 1;
> > > > > +       vio_info->vio_addr_high = (dbg0 & vio_dbgs->addr_h.mask) >>
> > > > > +                                 vio_dbgs->addr_h.start;
> > > >
> > > > What is vio_addr_high? As I know all register address are 32 bits, is
> > > > vio_addr_high the address above 32 bits?
> > >
> > > Yes, you are right. In MT6779, all register base are 32 bits. We can
> > > ignore this info for current driver. I'll update on next patch.
> > > Thanks !
> >
> > Such a strange hardware, all register is 32 bits but it has a
> > vio_addr_high in its register. OK, just drop this.
> >
> > >
> > > >
> > > > > +
> > > > > +       devapc_vio_info_print(ctx);
> > > > > +}
> > > > > +
> > > >