On 11/03/2011 11:56 AM, Marek Vasut wrote:
>> On 11/02/2011 07:15 PM, Marek Vasut wrote:
>>>> On 11/01/2011 05:54 PM, Marek Vasut wrote:
>>>>> +static void spl_onenand_get_geometry(struct spl_onenand_data *data)
>>>>> +{
>>>
>>> [...]
>>>
>>>>> + /* The page can be either 2k or 4k, avoid using DIV_ROUND_UP. */
>>>>> + if (data.pagesize == 2048) {
>>>>> + total_pages = len / 2048;
>>>>> + page = offset / 2048;
>>>>> + total_pages += !!(len & 2047);
>>>>> + } else if (data.pagesize == 4096) {
>>>>> + total_pages = len / 4096;
>>>>> + page = offset / 4096;
>>>>> + total_pages += !!(len & 4095);
>>>>> + }
>>>>
>>>> What's wrong with DIV_ROUND_UP? It should produce smaller code than
>>>> what you've done here...
>>>
>>> It pulls in aeabi_*div* functions, which won't fit into block 0 of
>>> Onenand.
>>
>> It shouldn't do that if the divisor is a constant power of 2. The
>> compiler will turn it into a shift, just like with the other divides in
>> the above code fragment.
>>
>> You can't use DIV_ROUND_UP directly on data.pagesize, but you can use it
>> in each branch of the if statement instead of that awkward and slightly
>> more expensive !!(len & 4095) construct.
>
> Expensive in what way?
Compare the resulting asm code. You're replacing this:
a = (b + 4095) >> 12;
with this:
a = b >> 12;
if (b & 4095)
a++;
> Either way, I don't think this matters that much.
This is code that has to fit in 1K -- why waste instructions by writing
code in a way that is *less* readable?
-Scott
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