linux-kernel - Re: [PATCH 3/4] UBI: use the whole MTD device size to get bad_peb

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Date:	Thu, 16 Aug 2012 11:25:07 +0300
From:	Shmulik Ladkani <shmulik.ladkani@...il.com>
To:	dedekind1@...il.com
Cc:	Richard Genoud <richard.genoud@...il.com>,
	David Woodhouse <dwmw2@...radead.org>,
	linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] UBI: use the whole MTD device size to get
 bad_peb_limit

Hi Artem, Richard,

On Wed, 15 Aug 2012 18:08:51 +0300 Artem Bityutskiy <dedekind1@...il.com> wrote:
> 1. Invalid blocks are block that contain one or more bad bits beyond
> ECC.

I would remove this one sentence from the log, it is misleading; invalid
blocks are not necessarily related to ECC.

>  		if (CONFIG_MTD_UBI_BEB_LIMIT > 0) {
> -			int percent = CONFIG_MTD_UBI_BEB_LIMIT;
> -			int limit = mult_frac(ubi->peb_count, percent, 100);
> +			int per1024 = CONFIG_MTD_UBI_BEB_LIMIT;
> +			int limit, device_pebs;
> +			uint64_t device_size;
> +
> +			/*
> +			 * Here we are using size of the entire flash chip and
> +			 * not just the MTD partition size because the maximum
> +			 * number of bad eraseblocks is a percentage of the
> +			 * whole device and bad eraseblocks are not fairly
> +			 * distributed over the flash chip. So the worst case
> +			 * is that all the bad eraseblocks of the chip are in
> +			 * the MTD partition we are attaching (ubi->mtd).
> +			 */
> +			device_size = mtd_get_device_size(ubi->mtd);
> +			device_pebs = mtd_div_by_eb(device_size, ubi->mtd);
> +			limit = mult_frac(device_pebs, per1024, 1024);
>  
>  			/* Round it up */
> -			if (mult_frac(limit, 100, percent) < ubi->peb_count)
> +			if (mult_frac(limit, 1024, per1024) < ubi->peb_count)

Oops... should be: 

+			if (mult_frac(limit, 1024, per1024) < device_pebs)

Regards,
Shmulik
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