linux-kernel - Re: [PATCH v3 1/2] mtd: nand: pxa3xx: Fix PIO FIFO draining

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Date:	Mon, 16 Feb 2015 13:57:12 -0300
From:	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>
To:	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
CC:	Gregory Clement <gregory.clement@...e-electrons.com>,
	Jason Cooper <jason@...edaemon.net>,
	Andrew Lunn <andrew@...n.ch>,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
	Brian Norris <computersforpeace@...il.com>,
	Lior Amsalem <alior@...vell.com>,
	Tawfik Bayouk <tawfik@...vell.com>,
	Thomas Petazzoni <thomas@...e-electrons.com>,
	Seif Mazareeb <seif@...vell.com>, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org,
	Sudhakar Gundubogula <sudhakar@...vell.com>,
	Nadav Haklai <nadavh@...vell.com>,
	Boris Brezillon <boris@...e-electrons.com>,
	linux-mtd@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 1/2] mtd: nand: pxa3xx: Fix PIO FIFO draining

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On 02/16/2015 01:41 PM, Maxime Ripard wrote:
> On Mon, Feb 16, 2015 at 05:27:53PM +0100, Thomas Petazzoni wrote:
>> Dear Maxime Ripard,
>>
>> On Mon, 16 Feb 2015 13:51:11 +0100, Maxime Ripard wrote:
>>
>>> +		while (index < (len * 4)) {
>>> +			u32 timeout;
>>> +
>>> +			__raw_readsl(info->mmio_base + NDDB, data + index, 8);
>>
>> Are you guaranteed that 'len' is a multiple of 32 bytes?
> 
> I don't know if you're guaranteed of anything, but the controller
> supports only 512, 2k, 4k and 8k pages, which are all mutiples of 32
> bytes.
> 

'len' here comes from:

do_bytes = min(info->data_size, info->chunk_size);

and

DIV_ROUND_UP(do_bytes, 4)

Where chunk_size is the size we want to read/write in each command step
(keep in mind that with extended commands we issue multiple commands, and
read/write data in chunks for each page).

And data_size is initialized at mtd->writesize (i.e. the size of a page).

Given all the flash pages I'm aware of are multiples of 32-bytes, and
given a chunk is either a quarter or half a page... I'd say it's
guaranteed to be 32-byte multiple, but perhaps it's a good idea to enforce it.
- -- 
Ezequiel García, Free Electrons
Embedded Linux, Kernel and Android Engineering
http://free-electrons.com
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