linux-kernel - Re: [PATCH 03/34] brcmfmac: firmware: Support having multiple alt paths

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Date:   Mon, 3 Jan 2022 04:26:17 +0300
From:   Dmitry Osipenko <digetx@...il.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>
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>,
        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 03/34] brcmfmac: firmware: Support having multiple alt
 paths

03.01.2022 03:41, Hector Martin пишет:
>> There is indeed no need for the castings in such cases, it's a typical
>> code pattern in kernel. You would need to do the casting for the other
>> way around, i.e. if char ** was returned and **alt_paths was a const.
> You do need to do the cast. Try it.
> 
> $ cat test.c
> int main() {
>         char *foo[1];
>         const char **bar = foo;
> 
>         return 0;
> }
> 
> $ gcc test.c
> test.c: In function ‘main’:
> test.c:4:28: warning: initialization of ‘const char **’ from
> incompatible pointer type ‘char **’ [-Wincompatible-pointer-types]
>     4 |         const char **bar = foo;
>       |
> 
> You can implicitly cast char* to const char*, but you *cannot*
> impliclicitly cast char** to const char** for the reason I explained. It
> requires a cast.

Right, I read it as "char * const *". The "const char **" vs "char *
const *" always confuses me.

Hence you should've written "const char **alt_paths;" in
brcm_alt_fw_paths() in the first place and then casting wouldn't have
been needed.