linux-kernel - Re: [PATCH 2/3] mtd: spi-nor: add support for Quad Page Program to no_sfdp

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Message-ID: <0203590f-d97c-61ab-eb31-3500b6c96ebb@microchip.com>
Date:   Fri, 29 Jul 2022 10:07:32 +0000
From:   <Tudor.Ambarus@...rochip.com>
To:     <ben.dooks@...ive.com>, <sudip.mukherjee@...ive.com>
CC:     <p.yadav@...com>, <michael@...le.cc>, <miquel.raynal@...tlin.com>,
        <richard@....at>, <vigneshr@...com>, <greentime.hu@...ive.com>,
        <jude.onyenegecha@...ive.com>, <william.salmon@...ive.com>,
        <adnan.chowdhury@...ive.com>, <linux-mtd@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] mtd: spi-nor: add support for Quad Page Program to
 no_sfdp_flags

On 7/29/22 11:10, Ben Dooks wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> On 29/07/2022 08:48, Tudor.Ambarus@...rochip.com wrote:
>> On 7/22/22 13:24, Sudip Mukherjee wrote:
>>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
>>>
>>> Hi Tudor,
>>>
>>
>> Hi!
>>
>>> On Mon, Jul 18, 2022 at 7:49 PM Sudip Mukherjee
>>> <sudip.mukherjee@...ive.com> wrote:
>>>>
>>>> On Mon, Jul 18, 2022 at 6:02 PM <Tudor.Ambarus@...rochip.com> wrote:
>>>>>
>>>>> On 7/12/22 19:38, Sudip Mukherjee wrote:
>>>>>> [You don't often get email from sudip.mukherjee@...ive.com. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
>>>>>>
>>>>>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
>>>>>>
>>>>>> Some flash chips which does not have a SFDP table can support Quad
>>>>>> Input Page Program. Enable it in hwcaps if defined.
>>>>>>
>>>>
>>>> <snip>
>>>>
>>>>>> diff --git a/drivers/mtd/spi-nor/core.h b/drivers/mtd/spi-nor/core.h
>>>>>> index 58fbedc94080f..dde636bdb1a7c 100644
>>>>>> --- a/drivers/mtd/spi-nor/core.h
>>>>>> +++ b/drivers/mtd/spi-nor/core.h
>>>>>> @@ -462,6 +462,7 @@ struct spi_nor_fixups {
>>>>>>    *   SPI_NOR_OCTAL_READ:      flash supports Octal Read.
>>>>>>    *   SPI_NOR_OCTAL_DTR_READ:  flash supports octal DTR Read.
>>>>>>    *   SPI_NOR_OCTAL_DTR_PP:    flash supports Octal DTR Page Program.
>>>>>> + *   SPI_NOR_QUAD_PP:         flash supports Quad Input Page Program.
>>>>>
>>>>> You don't need this flag if your flash supports the 4-byte Address
>>>>> Instruction Table. Does you flash support it? Can you dump all the
>>>>> SFDP tables, please?
>>>>
>>>> Not sure what the correct way to dump sfdp is. I did this from sysfs.
>>>
>>> I tried decoding this SFDP table and I think the parameters table says
>>> it has "3-Byte only addressing".
>>> So, I guess that means it does not support 4-byte Address Instruction
>>> Table. And the datasheet
>>> says it supports "Quad Input Page Program (3-byte Address)".
>>> My existing patchset works for Quad Input Page Program, and I can send
>>> a v2 with the previous
>>> patch and this merged together (as you suggested) or I can try
>>> enabling sfdp for this chip and then use
>>
>> You should definitely enable SFDP and get rid of the NO_SFDP_FLAGS flags,
>> regardless of the 1-1-4 PP outcome.
>>
>>> a fixup_flags to enable "Quad Input Page Program" which I think will
>>> be more complicated.
>>> Which one will you suggest?
>>>
>>
>> First I'd like to understand what "much better performance" means. Would
>> you run some speed tests please? mtd-utils should have a speedtest, otherwise
>> you can use the in kernel mtd_speedtest module. Page programs are slow anyway,
>> using 4 lines may not make any difference. But let's see.
>>
>> About your question, it depends on how common is 1-1-4 pp. If it's common and
>> desirable we can introduce a flash info flag.
> 
> We have an issue with the SPI controller where if it isn't in the above
> 1 bit modes it has to block the CPU as the feature to hold the clock is
> not enabled in the 1bit "old" modes. In the old modes, if the FIFO gets
> to the empty stage then the CS gets de-selected. If we can enable the
> 4bit mode, we can also set the clock-suspend flag which means the code
> does not have to block the core it is running on to ensure it gets the
> data out in time.

I'm not sure I understood your SPI controller limitation, but shouldn't
matter from a flash point of view anyway.
> 
> At the moment speed tests are not easy as we are on entirely emulated
> hardware, we could try some but the results may not represent what the
> real chip can perform.

Ok, then ignore the speed test suggestion. I've shuffled few vendor datasheets
and micron seems to use 1-1-4 PP too.

So I suggest to add SPI_NOR_QUAD_PP under nor->info->flags because 1-1-4 PP
is not SFDP discoverable. SPINOR_OP_PP_1_1_4_4B is and can be retrieved from
SFDP by parsing 4BAIT.
And please get rid of the no-sfdp-flags from the flash definition and use
instead PARSE_SFDP.

-- 
Cheers,
ta