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

[Jagan Teki]

On Mon, Oct 24, 2016 at 7:37 PM, Cyrille Pitchen
<cyrille.pitchen@xxxxxxxxx> wrote:
> Le 24/10/2016 Ã 14:09, Cyrille Pitchen a Ãcrit :
>> Hi Jagan,
>>
>> Le 24/10/2016 Ã 09:41, Jagan Teki a Ãcrit :
>>> On Sun, Oct 23, 2016 at 2:03 AM, Marek Vasut <marex@xxxxxxx> wrote:
>>>> On 10/22/2016 01:00 PM, Jagan Teki wrote:
>>>>> On Wed, Oct 5, 2016 at 5:30 PM, Cyrille Pitchen
>>>>> <cyrille.pitchen@xxxxxxxxx> 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.
>>
>> Hence most of the Micron n25q256* memories has no op code for 4-byte address
>> Page Program 1-1-1.
>> Then we could use the 34h op code instead to perform 4-byte address Page
>> Program 1-1-4 but some SPI controllers might not support the SPI 1-1-4 protocol
>> for Page Program operations. Sp entering the 4-byte address mode or using
>> the BAR might still be the only solutions in those cases.
>>
>> Also, I'm pretty sure some other SPI NOR memories support 4-byte address Fast
>> Read op codes but only 3-byte address op codes for Page Program and Sector
>> Erase. I will look at the datasheets I have to find and provide an example.
>>
>>
>
> Even worse, let's take the example for Macronix MX25L25635* and MX25L25673*:
> they both share the very same JEDEC ID. The older part (35) doesn't support
> the 4-byte address instruction set at all whereas the newer part (73) does.

So, though we have a support of 4-byte opcode, few of the reads will
still way back to use 3-byte opcode is it?
If ie the case may be we can directly rely on 4-byte opcode page
program or reads instead of creating check for which opcode support
which bytes address, IMHO.

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