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Subject: Re: [PATCH v3] net: stmmac: compare p->des0 and p->des1 with __le32
 type values
To:     Min-Hua Chen <minhuadotchen@gmail.com>, kuba@kernel.org
Cc:     alexandre.torgue@foss.st.com, davem@davemloft.net,
        edumazet@google.com, joabreu@synopsys.com,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-stm32@st-md-mailman.stormreply.com,
        mcoquelin.stm32@gmail.com, netdev@vger.kernel.org,
        pabeni@redhat.com, peppe.cavallaro@st.com,
        simon.horman@corigine.com
References: <20230519152715.7d1c3a49@kernel.org>
 <20230520015527.215952-1-minhuadotchen@gmail.com>
From:   Edward Cree <ecree.xilinx@gmail.com>
Message-ID: <9e6b813a-bc1a-6a39-904d-5c45f983cd23@gmail.com>
Date:   Mon, 22 May 2023 15:09:14 +0100
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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