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

[Cyrille Pitchen]

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.


Best regards,

Cyrille