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

Neal Liu
2020-08-11T02:44:38Z

Hi Chun-Kuang,

On Tue, 2020-08-11 at 07:14 +0800, Chun-Kuang Hu wrote:
> 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);
>

We set 0 to make sure all bits are cleared. But it won't cause any
problem if we remove it. I'll update on next patch.
Thanks !

> > >
> > > > + 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.

Okay.

>
> > >
> > > > +
> > > > + 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.
>

Okay, it make sense. I'll update on next patch.
Thanks !

> > >
> > > > + 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.

Okay, it make sense. I'll add stop_devapc() on next patch.
Thanks !

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