linux-kernel - Re: [PATCH v3] net: stmmac: compare p->des0 and p->des1 with _

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Message-ID: <9e6b813a-bc1a-6a39-904d-5c45f983cd23@gmail.com>
Date:   Mon, 22 May 2023 15:09:14 +0100
From:   Edward Cree <ecree.xilinx@...il.com>
To:     Min-Hua Chen <minhuadotchen@...il.com>, kuba@...nel.org
Cc:     alexandre.torgue@...s.st.com, davem@...emloft.net,
        edumazet@...gle.com, joabreu@...opsys.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com,
        mcoquelin.stm32@...il.com, netdev@...r.kernel.org,
        pabeni@...hat.com, peppe.cavallaro@...com,
        simon.horman@...igine.com
Subject: Re: [PATCH v3] net: stmmac: compare p->des0 and p->des1 with __le32
 type values

On 20/05/2023 02:55, Min-Hua Chen wrote:
>> On Fri, 19 May 2023 19:50:28 +0800 Min-Hua Chen wrote:
>>> -		if ((p->des0 == 0xffffffff) && (p->des1 == 0xffffffff))
>>> +		if (p->des0 == cpu_to_le32(0xffffffff) &&
>>> +		    p->des1 == cpu_to_le32(0xffffffff))
>>
>> Can you try to fix the sparse tool instead? I believe it already
>> ignores such errors for the constant of 0, maybe it can be taught 
>> to ignore all "isomorphic" values?
>>
> 
> I downloaded the source code of sparse and I'm afraid that I cannot make
> 0xFFFFFFFF ignored easily. I've tried ~0 instead of 0xFFFFFF,
> but it did not work with current sparse.
> 
> 0 is a special case mentioned in [1].

I believe you can do something like
    if ((p->des0 == ~(__le32)0) && (p->des1 == ~(__le32)0))
 and sparse will accept that, because the cast is allowed under the
 special case.
HTH,
-ed