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SubjectRe: [PATCH v2 net-next 1/3] net: dsa: lan9303: Refactor lan9303_xxx_packet_processing()
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On 01. aug. 2017 16:02, Andrew Lunn wrote:
> On Tue, Aug 01, 2017 at 03:50:14PM +0200, Egil Hjelmeland wrote:
>> On 01. aug. 2017 15:39, Andrew Lunn wrote:
>>>> @@ -704,7 +710,7 @@ static void lan9303_get_ethtool_stats(struct dsa_switch *ds, int port,
>>>> unsigned int u, poff;
>>>> int ret;
>>>> - poff = port * 0x400;
>>>> + poff = LAN9303_SWITCH_PORT_REG(port, 0);
>>>> for (u = 0; u < ARRAY_SIZE(lan9303_mib); u++) {
>>>> ret = lan9303_read_switch_reg(chip,
>>>
>>> So the actual code is:
>>>
>>> for (u = 0; u < ARRAY_SIZE(lan9303_mib); u++) {
>>> ret = lan9303_read_switch_reg(chip,
>>> lan9303_mib[u].offset + poff,
>>> &reg);
>>>
>>> Could this be written as
>>>
>>> for (u = 0; u < ARRAY_SIZE(lan9303_mib); u++) {
>>> ret = lan9303_read_switch_port(chip, port, lan9303_mib[u].offset, &reg);
>>>
>>> It is then clear you are reading the statistics from a port register.
>>>
>>> Andrew
>>>
>>
>> Yes it can. Since it is (insignificantly) less efficient, I
>> chose not to touch it. But I can do it if you like.
>
> I doubt it is less efficient. The compiler has seen
> lan9303_read_switch_port() and will probably inline it. So what the
> optimiser gets to see is probably the same in both cases.
>
> Try generating the assembler listing in both cases, and compare them
>
> make drivers/net/dsa/lan9303-core.lst
>
> Andrew
>

Thanks for the tips about generating assembler listing, can be useful
another time. But in this case I trust you :-)
And in this case it does not really matter, because its not in the
data path.

I did try to look at the listing. But I did not quite understand it.
Looks like it is doing both inlining and unrolling.

Anyway, you just decide how you like to have it in this series.

Egil



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