linux-kernel - Re: [PATCH v2 0/9] mtd: spi-nor: parse SFDP tables to setup (Q)SPI memories

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Message-ID: <CAD6G_RQc8JJefBP4=i721zTWShKrojKX2HWSJ+6EsgadL-Srww@mail.gmail.com>
Date:   Wed, 26 Oct 2016 01:29:52 +0530
From:   Jagan Teki <jagan@...nedev.com>
To:     Cyrille Pitchen <cyrille.pitchen@...el.com>
Cc:     Marek Vasut <marex@...x.de>,
        Brian Norris <computersforpeace@...il.com>,
        "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
        nicolas.ferre@...el.com, boris.brezillon@...e-electrons.com,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 0/9] mtd: spi-nor: parse SFDP tables to setup (Q)SPI memories

Hi Cyrille,

On Tue, Oct 25, 2016 at 2:38 PM, Jagan Teki <jagan@...nedev.com> wrote:
> On Mon, Oct 24, 2016 at 7:37 PM, Cyrille Pitchen
> <cyrille.pitchen@...el.com> wrote:
>> Le 24/10/2016 à 14:09, Cyrille Pitchen a écrit :
>>> Hi Jagan,
>>>
>>> Le 24/10/2016 à 09:41, Jagan Teki a écrit :
>>>> On Sun, Oct 23, 2016 at 2:03 AM, Marek Vasut <marex@...x.de> wrote:
>>>>> On 10/22/2016 01:00 PM, Jagan Teki wrote:
>>>>>> On Wed, Oct 5, 2016 at 5:30 PM, Cyrille Pitchen
>>>>>> <cyrille.pitchen@...el.com> wrote:
>>>>>>> Hi all,
>>>>>>>
>>>>>>> This series extends support of SPI protocols to new protocols such as
>>>>>>> SPI x-2-2 and SPI x-4-4. Also spi_nor_scan() tries now to select the right
>>>>>>> op codes, timing parameters (number of mode and dummy cycles) and erase
>>>>>>> sector size by parsing the Serial Flash Discoverable Parameter (SFDP)
>>>>>>> tables, when available, as defined in the JEDEC JESD216 specifications.
>>>>>>>
>>>>>>> When SFDP tables are not available, legacy settings are still used for
>>>>>>> backward compatibility (SPI and earlier QSPI memories).
>>>>>>>
>>>>>>> Support of SPI memories >128Mbits is also improved by using the 4byte
>>>>>>> address instruction set, when available. Using those dedicated op codes
>>>>>>> is stateless as opposed to enter the 4byte address mode, hence a better
>>>>>>> compatibility with some boot loaders which expect to use 3byte address
>>>>>>> op codes.
>>>>>>
>>>>>> The memories which are > 128Mbits should have 4-bytes addressing
>>>>>> support based on my experience, do you think BAR is also required
>>>>>> atleast from spi-nor side?
>>>>>
>>>>> Yes, I believe BAR is still required for broken/dumb flash chips.
>>>>> Not all chips > 16 MiB support dedicated 4-byte addressing opcodes :-(
>>>>
>>>> Do you have list for those broken chips? because I never find any
>>>> chips which has > 16 MiB with not support of 4-byte address opcodes
>>>> and I've seen the controller has dependable with BAR though it can
>>>> access > 16MiB ex: zynq qspi/
>>>>
>>>> thanks!
>>>>
>>>
>>> Let's take the case of Micron n25q256* memories. Depending of the part number,
>>> the 12h op code is associated with either 4-byte address Page Program 1-1-1
>>> or 3-byte address Page Program 1-4-4.
>>> Then considering parts where the 12h op code is used for 3-byte address Page
>>> Program 1-4-4, there is no op code for a 4-byte address Page Program 1-1-1.
>>>
>>> Note 15, extracted from the Micron n25q_256mb_3v_65nm.pdf datasheet, about
>>> the 3-byte address Page Program 1-4-4 (Extended Quad Input Fast Program):
>>> The code 38h is valid only for part numbers N25Q256A83ESF40x, N25Q256A83E1240x
>>> and N25Q256A83ESFA0F; the code 12h is valid for the other part numbers.

I am trying to understand the conflict more clearly with an example of
Micron, so on Table 18 from Micron n25q_256mb_3v_65nm.pdf datasheet,
Page program 3-byte has 02h and Quad page program 3-byte has 32h but
for 4-byte addressing only quad page program (no support of page
program) can be either 02h/32h/12h and indeed these can change based
on the n25q256* parts so why can't we rely on Quad page program for
4-byte addressing? and so there is no necessity for BAR here.

And also other than the un-supported-controller can't we rely directly
on supported page program opcodes for 4-byte addressing? say if it is
supporting QPP on 4-byte then use it as it is and no need to take care
of PP here.

thanks!
-- 
Jagan Teki
Free Software Engineer | www.openedev.com
U-Boot, Linux | Upstream Maintainer
Hyderabad, India.