linux-kernel - Re: [PATCH v3 2/2] soc: mediatek: add mtk-devapc driver

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Date:   Wed, 22 Jul 2020 07:21:35 +0800
From:   Chun-Kuang Hu <chunkuang.hu@...nel.org>
To:     Neal Liu <neal.liu@...iatek.com>
Cc:     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 v3 2/2] soc: mediatek: add mtk-devapc driver

Hi, Neal:

Neal Liu <neal.liu@...iatek.com> 於 2020年7月21日 週二 下午12:00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 *ctx, u32 vio_idx)

vio_idx is useless, so remove it.

> +{
> +       u32 vio_shift_sta;
> +       void __iomem *reg;
> +
> +       reg = ctx->devapc_pd_base + ctx->offset->vio_shift_sta;
> +       vio_shift_sta = readl(reg);
> +
> +       if (vio_shift_sta)
> +               return __ffs(vio_shift_sta);
> +
> +       return 31;
> +}
> +

[snip]

> +
> +/*
> + * mtk_devapc_dump_vio_dbg - get the violation index and dump the full violation
> + *                           debug information.
> + */
> +static bool mtk_devapc_dump_vio_dbg(struct mtk_devapc_context *ctx, u32 vio_idx)
> +{
> +       u32 shift_bit;
> +
> +       if (check_vio_mask(ctx, vio_idx))
> +               return false;
> +
> +       if (!check_vio_status(ctx, vio_idx))
> +               return false;
> +
> +       shift_bit = get_shift_group(ctx, vio_idx);
> +
> +       if (sync_vio_dbg(ctx, shift_bit))
> +               return false;
> +
> +       devapc_extract_vio_dbg(ctx);

I think get_shift_group(), sync_vio_dbg(), and
devapc_extract_vio_dbg() should be moved out of vio_idx for-loop (the
loop in devapc_violation_irq()) because these three function is not
related to vio_idx.
Another question: when multiple vio_idx violation occur, vio_addr is
related to which one vio_idx? The latest happened one?

> +
> +       return true;
> +}
> +
> +/*
> + * 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 *ctx)
> +{
> +       u32 vio_idx;
> +
> +       for (vio_idx = 0; vio_idx < ctx->vio_idx_num; vio_idx++) {
> +               if (!mtk_devapc_dump_vio_dbg(ctx, vio_idx))
> +                       continue;
> +
> +               /* Ensure that violation info are written before
> +                * further operations
> +                */
> +               smp_mb();
> +
> +               /*
> +                * Mask slave's irq before clearing vio status.
> +                * Must do it to avoid nested interrupt and prevent
> +                * unexpected behavior.
> +                */
> +               mask_module_irq(ctx, vio_idx, true);
> +
> +               clear_vio_status(ctx, vio_idx);
> +
> +               mask_module_irq(ctx, vio_idx, false);
> +       }
> +
> +       return IRQ_HANDLED;
> +}
> +
> +/*
> + * start_devapc - initialize devapc status and start receiving interrupt
> + *                while devapc violation is triggered.
> + */
> +static int start_devapc(struct mtk_devapc_context *ctx)
> +{
> +       void __iomem *pd_vio_shift_sta_reg;
> +       void __iomem *pd_apc_con_reg;
> +       u32 vio_shift_sta;
> +       u32 vio_idx;
> +
> +       pd_apc_con_reg = ctx->devapc_pd_base + ctx->offset->apc_con;
> +       pd_vio_shift_sta_reg = ctx->devapc_pd_base + ctx->offset->vio_shift_sta;
> +       if (!pd_apc_con_reg || !pd_vio_shift_sta_reg)
> +               return -EINVAL;
> +
> +       /* Clear devapc violation status */
> +       writel(BIT(31), pd_apc_con_reg);
> +
> +       /* Clear violation shift status */
> +       vio_shift_sta = readl(pd_vio_shift_sta_reg);
> +       if (vio_shift_sta)
> +               writel(vio_shift_sta, pd_vio_shift_sta_reg);
> +
> +       /* Clear slave violation status */
> +       for (vio_idx = 0; vio_idx < ctx->vio_idx_num; vio_idx++) {
> +               clear_vio_status(ctx, vio_idx);
> +               mask_module_irq(ctx, vio_idx, false);
> +       }
> +

Why do you clear these? After power on hardware, I think these
register status are correct. If the default value of these register
are not correct, add a comment for this.

Regards,
Chun-Kuang.

> +       return 0;
> +}
> +