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 for linux-mtd@lists.infradead.org; Mon, 10 Dec 2018 11:28:20 +0000
Subject: Re: [RFC PATCH 13/34] mtd: spi-nor: Add the concept of SPI NOR
 manufacturer driver
To: Boris Brezillon <boris.brezillon@bootlin.com>
CC: Tudor Ambarus <tudor.ambarus@microchip.com>, Marek Vasut
 <marek.vasut@gmail.com>, Yogesh Narayan Gaur <yogeshnarayan.gaur@nxp.com>,
 Miquel Raynal <miquel.raynal@bootlin.com>, David Woodhouse
 <dwmw2@infradead.org>, Brian Norris <computersforpeace@gmail.com>, Richard
 Weinberger <richard@nod.at>, <linux-mtd@lists.infradead.org>
References: <20181207092637.18687-1-boris.brezillon@bootlin.com>
 <20181207092637.18687-14-boris.brezillon@bootlin.com>
 <e0db2bce-df36-9068-cc41-149e9c919b1e@ti.com>
 <20181210093532.5b3de67a@bbrezillon>
From: Vignesh R <vigneshr@ti.com>
Message-ID: <ff61eec3-0f4c-2de1-b73d-23fc2396737b@ti.com>
Date: Mon, 10 Dec 2018 16:58:39 +0530
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On 10/12/18 2:05 PM, Boris Brezillon wrote:
> Hi Vignesh,
> 
> On Mon, 10 Dec 2018 13:50:03 +0530
> Vignesh R <vigneshr@ti.com> wrote:
> 
>>>  static const struct flash_info *spi_nor_read_id(struct spi_nor *nor)
>>>  {
>>>  	int			tmp;
>>> @@ -1734,13 +1751,21 @@ static const struct flash_info *spi_nor_read_id(struct spi_nor *nor)
>>>  		return ERR_PTR(tmp);
>>>  	}
>>>  
>>> -	for (tmp = 0; tmp < ARRAY_SIZE(spi_nor_ids) - 1; tmp++) {
>>> -		info = &spi_nor_ids[tmp];
>>> -		if (info->id_len) {
>>> -			if (!memcmp(info->id, id, info->id_len))
>>> -				return &spi_nor_ids[tmp];
>>> +	for (tmp = 0; tmp < ARRAY_SIZE(manufacturers); tmp++) {
>>> +		info = spi_nor_search_part_by_id(manufacturers[tmp]->parts,
>>> +						 manufacturers[tmp]->nparts,
>>> +						 id);  
>>
>> This could probably be optimized a bit by comparing manufacturer ID and
>> then looking through parts list of that particular manufacturer only.
>> (with expection of winbond manufacturer ID, where will have to go
>> through spansion parts list as well)
> 
> That's what I did at first, but it doesn't work. Some manufacturer IDs
> are prefixed by one or several continuation codes (0x7F). That was done
> to extend the 256 IDs space (see spec JEP106AX). We could have the
> manufacturer ID encoded with an array of byte instead of a single byte,
> but there's more: some flashes that are supposed to used continuation
> codes, just output the last (non-continuation) byte (see the ISSI IDs
> here [1] if you need a proof ;-)). So we're screwed.
> 

Thats bad.. Few ISSI IDs are in conflict with company that does not have
Continuation Code. Thanks for the information!

> Regards,
> 
> Boris
> 
> [1]https://elixir.bootlin.com/linux/v4.20-rc6/source/drivers/mtd/spi-nor/spi-nor.c#L1351
> 

-- 
Regards
Vignesh