Re: [PATCH v5 2/2] soc: mediatek: add mt6779 devapc driver

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

Hi, Neal:

Neal Liu <neal.liu@mediatek.com> 於 2020年8月10日 週一 上午11:43寫道：
>
> Hi Chun-Kuang,
>
> On Fri, 2020-08-07 at 23:52 +0800, Chun-Kuang Hu wrote:
> > Hi, Neal:
> >
> > Neal Liu <neal.liu@mediatek.com> 於 2020年8月7日 週五 上午10:34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]
> >
> > > +
> > > +#define PHY_DEVAPC_TIMEOUT     0x10000
> > > +
> > > +/*
> > > + * devapc_sync_vio_dbg - do "shift" mechansim" to get full violation information.
> > > + *                       shift mechanism is depends on devapc hardware design.
> > > + *                       Mediatek devapc set multiple slaves as a group.
> > > + *                       When violation is triggered, violation info is kept
> > > + *                       inside devapc hardware.
> > > + *                       Driver should do shift mechansim to sync full violation
> > > + *                       info to VIO_DBGs registers.
> > > + *
> > > + */
> > > +static int devapc_sync_vio_dbg(struct mtk_devapc_context *ctx)
> > > +{
> > > +       void __iomem *pd_vio_shift_sta_reg;
> > > +       void __iomem *pd_vio_shift_sel_reg;
> > > +       void __iomem *pd_vio_shift_con_reg;
> > > +       int min_shift_group;
> > > +       int ret;
> > > +       u32 val;
> > > +
> > > +       pd_vio_shift_sta_reg = ctx->infra_base +
> > > +                              ctx->data->vio_shift_sta_offset;
> > > +       pd_vio_shift_sel_reg = ctx->infra_base +
> > > +                              ctx->data->vio_shift_sel_offset;
> > > +       pd_vio_shift_con_reg = ctx->infra_base +
> > > +                              ctx->data->vio_shift_con_offset;
> > > +
> > > +       /* Find the minimum shift group which has violation */
> > > +       val = readl(pd_vio_shift_sta_reg);
> > > +       if (!val)
> > > +               return false;
> > > +
> > > +       min_shift_group = __ffs(val);
> > > +
> > > +       /* Assign the group to sync */
> > > +       writel(0x1 << min_shift_group, pd_vio_shift_sel_reg);
> > > +
> > > +       /* Start syncing */
> > > +       writel(0x1, pd_vio_shift_con_reg);
> > > +
> > > +       ret = readl_poll_timeout(pd_vio_shift_con_reg, val, val == 0x3, 0,
> > > +                                PHY_DEVAPC_TIMEOUT);
> > > +       if (ret) {
> > > +               dev_err(ctx->dev, "%s: Shift violation info failed\n", __func__);
> > > +               return false;
> > > +       }
> > > +
> > > +       /* Stop syncing */
> > > +       writel(0x0, pd_vio_shift_con_reg);
> > > +       writel(0x0, pd_vio_shift_sel_reg);
> >
> > This is redundant because you set this register before start syncing.
>
> No, we don't set this reg before start syncing.
>

I'm talking about pd_vio_shift_sel_reg, and I find this before start syncing:

       /* Assign the group to sync */
       writel(0x1 << min_shift_group, pd_vio_shift_sel_reg);

       /* Start syncing */
       writel(0x1, pd_vio_shift_con_reg);

> >
> > > +       writel(0x1 << min_shift_group, pd_vio_shift_sta_reg);
> >
> > You read this register to find minimum shift group, but you write it
> > back into this register, so this function would get the same minimum
> > shift group in next time, isn't it?
>
> No. The operation means write clear. We won't get the same minimum shift
> group after clear this bit.
>

Add comment for this because this is not trivial.

> >
> > > +
> > > +       return true;
> > > +}
> > > +
> > > +/*
> > > + * devapc_extract_vio_dbg - extract full violation information after doing
> > > + *                          shift mechanism.
> > > + */
> > > +static void devapc_extract_vio_dbg(struct mtk_devapc_context *ctx)
> > > +{
> > > +       struct mtk_devapc_vio_dbgs *vio_dbgs;
> >
> > struct mtk_devapc_vio_dbgs vio_dbgs;
> >
> > Use stack instead of allocating from heap.
>
> Why it cannot use heap if the memory is handled correctly?
>

You could use heap but allocating memory from heap would cost much
time. In the worst case, it would trigger buddy system to break a page
for slub. Using stack cost almost no time, but it has some limitation.
Stack memory is small and it should be used for local variable, and
vio_dbgs match this limitation, so stack is better than heap.

> >
> > > +       void __iomem *vio_dbg0_reg;
> > > +       void __iomem *vio_dbg1_reg;
> > > +
> > > +       vio_dbgs = devm_kzalloc(ctx->dev, sizeof(struct mtk_devapc_vio_dbgs),
> > > +                               GFP_KERNEL);
> > > +       if (!vio_dbgs)
> > > +               return;
> > > +
> > > +       vio_dbg0_reg = ctx->infra_base + ctx->data->vio_dbg0_offset;
> > > +       vio_dbg1_reg = ctx->infra_base + ctx->data->vio_dbg1_offset;
> > > +
> > > +       vio_dbgs->vio_dbg0 = readl(vio_dbg0_reg);
> > > +       vio_dbgs->vio_dbg1 = readl(vio_dbg1_reg);
> > > +
> > > +       /* Print violation information */
> > > +       if (vio_dbgs->dbg0_bits.vio_w)
> > > +               dev_info(ctx->dev, "Write Violation\n");
> > > +       else if (vio_dbgs->dbg0_bits.vio_r)
> > > +               dev_info(ctx->dev, "Read Violation\n");
> > > +
> > > +       dev_info(ctx->dev, "Bus ID:0x%x, Dom ID:0x%x, Vio Addr:0x%x\n",
> > > +                vio_dbgs->dbg0_bits.mstid, vio_dbgs->dbg0_bits.dmnid,
> > > +                vio_dbgs->vio_dbg1);
> > > +}
> > > +
> >
> > [snip]
> >
> > > +
> > > +static int mtk_devapc_probe(struct platform_device *pdev)
> > > +{
> > > +       struct device_node *node = pdev->dev.of_node;
> > > +       struct mtk_devapc_context *ctx;
> > > +       u32 devapc_irq;
> > > +       int ret;
> > > +
> > > +       if (IS_ERR(node))
> > > +               return -ENODEV;
> > > +
> > > +       ctx = devm_kzalloc(&pdev->dev, sizeof(*ctx), GFP_KERNEL);
> > > +       if (!ctx)
> > > +               return -ENOMEM;
> > > +
> > > +       ctx->data = of_device_get_match_data(&pdev->dev);
> > > +       ctx->dev = &pdev->dev;
> > > +
> > > +       ctx->infra_base = of_iomap(node, 0);
> > > +       if (!ctx->infra_base)
> > > +               return -EINVAL;
> > > +
> > > +       devapc_irq = irq_of_parse_and_map(node, 0);
> > > +       if (!devapc_irq)
> > > +               return -EINVAL;
> > > +
> > > +       ctx->infra_clk = devm_clk_get(&pdev->dev, "devapc-infra-clock");
> > > +       if (IS_ERR(ctx->infra_clk))
> > > +               return -EINVAL;
> > > +
> > > +       if (clk_prepare_enable(ctx->infra_clk))
> > > +               return -EINVAL;
> > > +
> > > +       ret = devm_request_irq(&pdev->dev, devapc_irq,
> > > +                              (irq_handler_t)devapc_violation_irq,
> > > +                              IRQF_TRIGGER_NONE, "devapc", ctx);
> > > +       if (ret) {
> > > +               clk_disable_unprepare(ctx->infra_clk);
> > > +               return ret;
> > > +       }
> > > +
> > > +       platform_set_drvdata(pdev, ctx);
> > > +
> > > +       start_devapc(ctx);
> > > +
> > > +       return 0;
> > > +}
> > > +
> > > +static int mtk_devapc_remove(struct platform_device *pdev)
> > > +{
> > > +       struct mtk_devapc_context *ctx = platform_get_drvdata(pdev);
> > > +
> >
> > stop_devapc(ctx);
>
> We don't have to do any further operations to stop devapc hw.
>

After this driver is removed, I think we should restore hardware to
the status before probing. Before probe(), devapc hardware is stopped
(pd_apc_con_reg is a default value and all vio irq is masked), so it
should be the same status after remove(). This concept is the same as
what you do for infra_clk.

Regards,
Chun-Kuang.

> >
> > Regards,
> > Chun-Kuang.
> >
> > > +       if (ctx->infra_clk)
> > > +               clk_disable_unprepare(ctx->infra_clk);
> > > +
> > > +       return 0;
> > > +}
> > > +
>