netdev - Re: [PATCH v2 17/35] brcmfmac: pcie: Provide a buffer of random bytes to the device

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Message-ID: <86f0c8a6-5c58-e59f-9198-934ed2f12a7f@broadcom.com>
Date:   Mon, 10 Jan 2022 12:28:05 +0100
From:   Arend van Spriel <arend.vanspriel@...adcom.com>
To:     Hector Martin <marcan@...can.st>,
        Kalle Valo <kvalo@...eaurora.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>,
        Arend van Spriel <aspriel@...il.com>,
        Franky Lin <franky.lin@...adcom.com>,
        Hante Meuleman <hante.meuleman@...adcom.com>,
        Chi-hsien Lin <chi-hsien.lin@...ineon.com>,
        Wright Feng <wright.feng@...ineon.com>,
        Dmitry Osipenko <digetx@...il.com>
Cc:     Sven Peter <sven@...npeter.dev>,
        Alyssa Rosenzweig <alyssa@...enzweig.io>,
        Mark Kettenis <kettenis@...nbsd.org>,
        Rafał Miłecki <zajec5@...il.com>,
        Pieter-Paul Giesberts <pieter-paul.giesberts@...adcom.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Hans de Goede <hdegoede@...hat.com>,
        "John W. Linville" <linville@...driver.com>,
        "brian m. carlson" <sandals@...stytoothpaste.net>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-acpi@...r.kernel.org, brcm80211-dev-list.pdl@...adcom.com,
        SHA-cyfmac-dev-list@...ineon.com
Subject: Re: [PATCH v2 17/35] brcmfmac: pcie: Provide a buffer of random bytes
 to the device

On 1/10/2022 12:09 PM, Hector Martin wrote:
> On 2022/01/10 18:11, Arend van Spriel wrote:
>> On 1/4/2022 8:26 AM, Hector Martin wrote:
>>> Newer Apple firmwares on chipsets without a hardware RNG require the
>>> host to provide a buffer of 256 random bytes to the device on
>>> initialization. This buffer is present immediately before NVRAM,
>>> suffixed by a footer containing a magic number and the buffer length.
>>>
>>> This won't affect chips/firmwares that do not use this feature, so do it
>>> unconditionally.
>>
>> Not sure what the general opinion is here, but pulling random bytes for
>> naught seems wasteful to me. So if there is a way of knowing it is
>> needed please make it conditional.
> 
> We could gate it on specific chips only, if you don't mind maintaining a
> list of those. AIUI that would be all the T2 platform chips or so (the
> newer two don't seem to need it).
> 
> Alternatively we could just do this only if an Apple OTP is detected.
> That is already implicitly gated by the OTP offset chip list.

That sounds like a good approach.

Regards,
Arend

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