linux-kernel - Re: [PATCH v4 7/7] soc: renesas: Add L2 cache management for RZ/Five SoC

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Date:   Mon, 28 Nov 2022 23:58:01 -0600
From:   Samuel Holland <samuel@...lland.org>
To:     "Lad, Prabhakar" <prabhakar.csengg@...il.com>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Magnus Damm <magnus.damm@...il.com>,
        Heiko Stuebner <heiko@...ech.de>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor.dooley@...rochip.com>,
        Guo Ren <guoren@...nel.org>,
        Jisheng Zhang <jszhang@...nel.org>,
        Atish Patra <atishp@...osinc.com>,
        Anup Patel <apatel@...tanamicro.com>,
        Andrew Jones <ajones@...tanamicro.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Philipp Tomsich <philipp.tomsich@...ll.eu>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org, linux-renesas-soc@...r.kernel.org,
        Biju Das <biju.das.jz@...renesas.com>,
        Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: Re: [PATCH v4 7/7] soc: renesas: Add L2 cache management for RZ/Five
 SoC

On 11/26/22 15:09, Lad, Prabhakar wrote:
>>> +     if (!ax45mp_priv->l2c_base) {
>>> +             ret = -ENOMEM;
>>> +             goto l2c_err;
>>> +     }
>>> +
>>> +     ret = ax45mp_configure_l2_cache(np);
>>> +     if (ret)
>>> +             goto l2c_err;
>>> +
>>> +     ret = ax45mp_configure_pma_regions(np);
>>> +     if (ret)
>>> +             goto l2c_err;
>>> +
>>> +     static_branch_disable(&ax45mp_l2c_configured);
>>
>> Instead of enabling this before the probe function, and disabling it
>> afterward, just enable it once here, in the success case. Then you can
>> drop the !ax45mp_priv check in the functions above.
>>
> I think I had tried it but static_branch_unlikely() was always returning true.

You use DEFINE_STATIC_KEY_FALSE above, so static_branch_unlikely()
should return false until you call static_branch_enable().

>> And none of the functions would get called anyway if the alternative is
>> not applied. I suppose it's not possible to do some of this probe logic
>> in the alternative check function?
>>
> you mean to check in the vendor errata patch function to see if this
> driver has probed?

I meant to do the equivalent of:

+     ax45mp_priv->ucctl_ok = ax45mp_cpu_cache_controlable();
+     ax45mp_priv->l2cache_enabled = ax45mp_cpu_l2c_ctl_status() &
AX45MP_L2_CACHE_CTL_CEN_MASK;

in the errata function, since that decides if the cache maintenance
functions actually do anything. But ax45mp_cpu_l2c_ctl_status() gets the
MMIO address from the DT, and trying to do that from the errata function
could get ugly, so maybe it is not a good suggestion.

Regards,
Samuel