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 下午12:01寫道：
>
> Hi Chun-Kuang,
>
> On Sat, 2020-08-01 at 08:12 +0800, Chun-Kuang Hu wrote:
> > Hi, Neal:
> >
> > This patch is for "mediatek,mt6779-devapc", so I think commit title
> > should show the SoC ID.
>
> Okay, I'll change title to 'soc:mediatek: add mt6779 devapc driver'.
>
> >
> > 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]
> >
> > > +
> > > +struct mtk_devapc_context {
> > > +       struct device *dev;
> > > +       u32 vio_idx_num;
> > > +       void __iomem *devapc_pd_base;
> > > +       struct mtk_devapc_vio_info *vio_info;
> > > +       const struct mtk_devapc_pd_offset *offset;
> > > +       const struct mtk_devapc_vio_dbgs *vio_dbgs;
> > > +};
> >
> > I think this structure should separate the constant part. The constant part is:
> >
> > struct mtk_devapc_data {
> >     const u32 vio_idx_num;
> >     const struct mtk_devapc_pd_offset *offset; /* I would like to
> > remove struct mtk_devapc_pd_offset and directly put its member into
> > this structure */
> >     const struct mtk_devapc_vio_dbgs *vio_dbgs; /* This may disappear */
> > };
> >
> > And the context is:
> >
> > struct mtk_devapc_context {
> >     struct device *dev;
> >     void __iomem *devapc_pd_base;
> >     const struct mtk_devapc_data *data;
> > };
> >
> > So when you define this, you would not waste memory to store non-constant data.
> >
> > static const struct mtk_devapc_data devapc_mt6779 = {
> >  .vio_idx_num = 510,
> >  .offset = &mt6779_pd_offset,
> >  .vio_dbgs = &mt6779_vio_dbgs,
> > };
> >
>
> Sorry, I still don't understand why this refactoring will not waste
> memory to store non-constant data. Could you explain more details?
> To my understanding, we still also have to allocate memory to store dev
> & devapc_pd_base.

In some situation, it is. You make the non-constant data a global
variable. I think the context data should be dynamic allocated. If
this driver is not probed, the non-constant data occupy the memory.

Regards,
Chun-Kuang.

>
> > Regards,
> > Chun-Kuang.
> >
> > > +
> > > +#endif /* __MTK_DEVAPC_H__ */
> > > --
> > > 1.7.9.5
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>