linux-kernel - Re: [PATCH 2/2] uio:powerpc:mpc85xx: l2-cache-sram uio driver implementation

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Date:   Tue, 14 Jun 2022 07:53:46 +0000
From:   Wenhu Wang <wenhu.wang@...mail.com>
To:     Christophe Leroy <christophe.leroy@...roup.eu>,
        Greg KH <gregkh@...uxfoundation.org>
CC:     "mpe@...erman.id.au" <mpe@...erman.id.au>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] uio:powerpc:mpc85xx: l2-cache-sram uio driver
 implementation

>> >> +
>> >> +struct mpc85xx_l2ctlr {
>> >> +     u32     ctl;            /* 0x000 - L2 control */
>> >
>> >What is the endian of these u32 values?  You map them directly to
>> >memory, so they must be specified some way, right?  Please make it
>> >obvious what they are.
>> >
>>
>> Surely, the values should be u32 here, modified in v2
>> The controller info could be found in
>> "QorIQ⑩ P2020 Integrated Processor Reference Manual"
>> "Chapter 6 L2 Look-Aside Cache/SRAM"
>> See: http://m4udit.dinauz.org/P2020RM_rev0.pdf
>
>That's not the answer to my question :)
>
>These are big-endian, right?  Please mark them as such and access them
>properly with the correct functions.

Yes, they are big-edian.
Does it work to add comments(about order and access functions) for the structure ahead of it？
And appending like "_be", "_access_be" or "_big_endian"? (struct mpc85xx_l2ctlr_be {ˇˇ};

>Tabs in Linux are always 8 spaces wide.
>

I will re-confirm the v2 of identation.

>>
>> I looked at that patch.
>>
>> I don't think you can just drop the #ifdef in function
>> __access_remote_vm() in mm/memory.c
>>
>> You have to replace it with something like:
>>
>>      if (!IS_ENABLED(CONFIG_HAVE_IOREMAP_PROT))
>>          break;
>>
>
>
>Another thing in that patch:
>
>By making generic_access_phys() a static inline, it means that everytime
>you refer to the address of that function in a vm_operations_struct
>struct, the compiler has to provide an outlined instance of the
>function. It means you'll likely have several instances of a
>generic_access_phys().
>
>What you could do instead is to add the following at the start of
>generic_access_phys() in mm/memory.c :
>
>        if (!IS_ENABLED(CONFIG_HAVE_IOREMAP_PROT))
>                return 0;
>

It is really a better chmoce, thanks for the advice.
Multiple instances exist as you mentioned, the block returns 0 with no-op
instance which makes no difference with the function return value.

I will update the patch after a re-confirming.

Thanks,
Wenhu