linux-kernel - Re: RE: [EXTERNAL] Re: [PATCH v10] ASoC: tas2781: Add tas2781 driver

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Date:   Thu, 6 Apr 2023 20:35:41 +0200
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     "Ding, Shenghao" <shenghao-ding@...com>,
        Amadeusz Slawinski <amadeuszx.slawinski@...ux.intel.com>
Cc:     "Lu, Kevin" <kevin-lu@...com>,
        "alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Xu, Baojun" <x1077012@...com>, "Gupta, Peeyush" <peeyush@...com>,
        "Navada Kanyana, Mukund" <navada@...com>,
        Shenghao Ding <13916275206@....com>,
        "broonie@...nel.org" <broonie@...nel.org>,
        "lgirdwood@...il.com" <lgirdwood@...il.com>,
        "perex@...ex.cz" <perex@...ex.cz>,
        "pierre-louis.bossart@...ux.intel.com" 
        <pierre-louis.bossart@...ux.intel.com>
Subject: Re: RE: [EXTERNAL] Re: [PATCH v10] ASoC: tas2781: Add tas2781 driver

Le 05/04/2023 à 13:21, Ding, Shenghao a écrit :
> Hi Both
> I wrote a test code to verify the be32_to_cpu & be32_to_cpup,
> static int __init lkm_init(void)
> {
> 	char test_buf[]={0x12, 0x34, 0xab, 0xbc, 0x56, 0x78, 0xef};
> 	unsigned int *k, p, q;
> 	int i;
> 
> 	printk("Hello, Shanghai!\n");
> 
> 	for (i = 0; i < 4; i ++) {
> 		k = (unsigned int *)&test_buf[i];
> 		p = be32_to_cpup((__be32 *)k);
> 		q = be32_to_cpu(test_buf[i]);
> 		printk("%d: *k = 0x%08x p = 0x%08x q = 0x%08x %ld\n",
> 			i, *k, p, q, sizeof(unsigned int));
> 	}
> 	return 0;
> }
> The output is:
> [ 9109.722548] Hello, Shanghai!
> [ 9109.726287] 0: *k = 0xbcab3412 p = 0x1234abbc q = 0x12000000 4
> [ 9109.727665] 1: *k = 0x56bcab34 p = 0x34abbc56 q = 0x34000000 4
> [ 9109.728553] 2: *k = 0x7856bcab p = 0xabbc5678 q = 0xabffffff 4
> [ 9109.729308] 3: *k = 0xef7856bc p = 0xbc5678ef q = 0xbcffffff 4
> Apparently, be32_to_cpup's output is what I expected.
> Looking forward to your comments. Thanks.

Hi,

thanks for the clarification and code sample.
You are right.

I had in mind that something like: be32_to_cpu((__be32 *)data);
would make it. (thanks to the cast)

But because of the need of "&" and "[offset]", it would just make the 
code unnecessarily complex.

I think that your approach is better.

CJ