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From: Dmitry Torokhov <dmitry.torokhov@gmail.com>
To: "Stéphane Chatty" <chatty@enac.fr>
Cc: ynezz@true.cz, linux-input@vger.kernel.org
Subject: Re: [PATCH] Support for 3M multitouch panel
Date: Tue, 22 Dec 2009 10:56:29 -0800
Message-ID: <20091222185628.GA28392@core.coreip.homeip.net> (raw)
In-Reply-To: <694242AB-D4DC-470D-916D-9ADB2B798FBA@enac.fr>

Hi Stéphane,

On Tue, Dec 22, 2009 at 07:00:49PM +0100, Stéphane Chatty wrote:
> Hi Dmitry,
>
> I am working on the 3M driver and taking your comments into account (and 
> applying them to the Stantum driver as well) but I have an question on 
> the comment below:
>
>>
>>> +struct mmm_finger {
>>> +	__s32 x, y;
>>> +	__u8 rank;
>>> +	int touch:1, valid:1;
>>> +};
>>
>> Does it make sense to turn access to touch and valid into
>> read-modify-write sequence?  Just change them to be 'bool's, it won't
>> cause your structures to grow in size.
>>
>>> +struct mmm_data {
>>> +	struct mmm_finger f[10];
>>> +	__u8 curid, num;
>>> +	int touch:1, valid:1;
>>
>> Same as above.
>
> Why do you think a read-modify-write sequence would be better? in my  
> mind these were just cached values, just like x and y.

I meant "read-modify-write" is worse.

To modify a bitfiled the processor has to fetch data from memory (or
cache if it is in cache) perform a logical operation on it, and store
it back in teh memory. With boolean occupying 1 byte, on most
architectures (older alphas is one exception I know of) var=true can be
done by simple store, no need for "read-modify" part.

-- 
Dmitry
--
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  reply index

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2009-12-11 10:12 Stephane Chatty
2009-12-11 12:42 ` Petr Štetiar
2009-12-11 14:10   ` Fwd: " Stephane Chatty
2009-12-11 22:36     ` Dmitry Torokhov
2009-12-12  8:13       ` Stéphane Chatty
2009-12-12  8:30         ` Dmitry Torokhov
2009-12-22 18:00       ` Stéphane Chatty
2009-12-22 18:56         ` Dmitry Torokhov [this message]
2009-12-22 19:27           ` Stéphane Chatty
2009-12-22 22:04           ` Stephane Chatty
2009-12-23  0:22             ` Jiri Kosina
2009-12-23  0:33             ` Jiri Kosina
2009-12-23  9:47               ` Stéphane Chatty

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