linux-kernel - Re: [RFC V1 5/8] smi2021: Add smi2021

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Message-ID: <87620p3wzr.fsf@nemi.mork.no>
Date:	Mon, 18 Mar 2013 09:58:32 +0100
From:	Bjørn Mork <bjorn@...k.no>
To:	Hans Verkuil <hverkuil@...all.nl>
Cc:	Jon Arne Jørgensen <jonarne@...arne.no>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	elezegarcia@...il.com
Subject: Re: [RFC V1 5/8] smi2021: Add smi2021_video.c

Hans Verkuil <hverkuil@...all.nl> writes:

>> +/*
>> + *
>> + * The device delivers data in chunks of 0x400 bytes.
>> + * The four first bytes is a magic header to identify the chunks.
>> + *	0xaa 0xaa 0x00 0x00 = saa7113 Active Video Data
>> + *	0xaa 0xaa 0x00 0x01 = PCM - 24Bit 2 Channel audio data
>> + */
>> +static void process_packet(struct smi2021_dev *dev, u8 *p, int len)
>> +{
>> +	int i;
>> +	u32 *header;
>> +
>> +	if (len % 0x400 != 0) {
>> +		printk_ratelimited(KERN_INFO "smi2021::%s: len: %d\n",
>> +				__func__, len);
>> +		return;
>> +	}
>> +
>> +	for (i = 0; i < len; i += 0x400) {
>> +		header = (u32 *)(p + i);
>> +		switch (__cpu_to_be32(*header)) {
>
> That's not right. You probably mean __be32_to_cpu, that makes more sense.
>
>> +		case 0xaaaa0000: {
>> +			parse_video(dev, p+i+4, 0x400-4);
>> +			break;
>> +		}
>> +		case 0xaaaa0001: {
>> +			smi2021_audio(dev, p+i+4, 0x400-4);
>> +			break;
>> +		}

This could be just me, but I would have done it like this to take
advantage of compile time constant conversions (and also dropping the
noisy extra {}s):

		switch (*header) {
		case cpu_to_be32(0xaaaa0000):
			parse_video(dev, p+i+4, 0x400-4);
			break;
		case cpu_to_be32(0xaaaa0001):
			smi2021_audio(dev, p+i+4, 0x400-4);
			break;
                ..


>From the name of the function I assume the difference may actually be
measurable here if this runs for every processed packet.


Bjørn
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