netdev - Re: [PATCH] net: tg3: tidy up loop, remove need to compute off with a multiply

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Date:   Fri, 08 May 2020 16:21:46 -0700
From:   Joe Perches <joe@...ches.com>
To:     Colin King <colin.king@...onical.com>,
        Siva Reddy Kallam <siva.kallam@...adcom.com>,
        Prashant Sreedharan <prashant@...adcom.com>,
        Michael Chan <mchan@...adcom.com>,
        "David S . Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: tg3: tidy up loop, remove need to compute off with
 a multiply

On Fri, 2020-05-08 at 23:53 +0100, Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
> 
> Currently the value for 'off' is computed using a multiplication and
> a couple of statements later off is being incremented by len and
> this value is never read.  Clean up the code by removing the
> multiplication and just increment off by len on each iteration. Also
> use len instead of TG3_OCIR_LEN.

I think this is a lot harder to read.

> diff --git a/drivers/net/ethernet/broadcom/tg3.c b/drivers/net/ethernet/broadcom/tg3.c
[]
> @@ -10798,16 +10798,14 @@ static int tg3_init_hw(struct tg3 *tp, bool reset_phy)
>  static void tg3_sd_scan_scratchpad(struct tg3 *tp, struct tg3_ocir *ocir)
>  {
>  	int i;
> +	u32 off, len = TG3_OCIR_LEN;
>  
> -	for (i = 0; i < TG3_SD_NUM_RECS; i++, ocir++) {
> -		u32 off = i * TG3_OCIR_LEN, len = TG3_OCIR_LEN;
> -
> +	for (i = 0, off = 0; i < TG3_SD_NUM_RECS; i++, ocir++, off += len) {
>  		tg3_ape_scratchpad_read(tp, (u32 *) ocir, off, len);
> -		off += len;
>  
>  		if (ocir->signature != TG3_OCIR_SIG_MAGIC ||
>  		    !(ocir->version_flags & TG3_OCIR_FLAG_ACTIVE))
> -			memset(ocir, 0, TG3_OCIR_LEN);
> +			memset(ocir, 0, len);
>  	}
>  }

My preference would be for

{
	int i;
	u32 off = 0;

	for (i = 0; i < TG3_SD_NUM_RECS; i++) {
		tg3_ape_scratchpad_read(tp, (u32 *)ocir, off, TC3_OCIR_LEN);

		if (ocir->signature != TG3_OCIR_SIG_MAGIC ||
		    !(ocir->version_flags & TG3_OCIR_FLAG_ACTIVE))
			memset(ocir, 0, TG3_OCIR_LEN);

		off += TG3_OCIR_LEN;
		ocir++;
	}