Hi William,Right it does not impact our fast path: controller based ecc read/write. But things like on-chip ecc nand driver that uses exec_op API get impacted badly. We need to add nand op parser, several matching rules and other logics to use fast path page read/write instead of the low level data register read/write.
william.zhang@xxxxxxxxxxxx wrote on Mon, 12 Jun 2023 12:18:58 -0700:
On 06/12/2023 10:53 AM, Miquel Raynal wrote:
Hello again,Yes this is the patch what our exec_op work is based on. Thanks Boris! The issue with patch is that performance is very slow for anything that rely on nand_read_page_op as the patch implementing it using the low level cmd and data register to transfer the data byte by byte.
Perhaps we could have a single function that is statically assigned at
probe time instead of a first helper with two conditions which calls in
one case another hook... This can be simplified I guess.
>> Well this will need to be done at the SoC specific implementation level (bcm<xxx>_nand.c) and each SoC will need to have either general data bus read func with is_param option or data_bus_read_page, data_bus_read_param.
You told me in case we would use exec_op we could avoid the param
cache. If that's true then the whole support can be simplified.
>> Correct we may possibly unified the parameter data read but exec_op is long shot and we are not fully ready for that yet. It also depends on if the low level data register has endianess difference for the parameter data between difference SoCs.
So I would like to push the current implementation and we can explore the exec_op option late which will be a much big and complete different implementation.
I am sorry but this series is totally backwards, you're trying to guess
what comes next with the 'is_param' thing, it's exactly what we are
fighting against since 2017. There are plenty of ->exec_op()
conversions out there, I don't believe this one will be harder. You
need to convert the driver to this new API and get rid of this whole
endianness non-sense to simplify a lot the driver.
>>> I am not guessing anything but just factor out the existing common nand cache read logic into the single default function(or one for page read and another for parameter read as I mentioned in another thread) and allow SoC to overrides the implementation when needed.
No, you are trying to guess what type of read the core is performing,
either a regular data page read or a parameter page read.
I agree ->exec_op can possibly get rid of the parameter page read function and is the way to go. But it won't help on the page read for endianess.
You told me there is no endianess issue with the data pages, so why it
won't help on the page read?
It's not that I am against exec_op but I want to take one step a time
and I'd like to get these fixes
I don't see any fix here? Let me know if I am missing something but
right now I see a new version of the controller being supported with
its own constraints. If you are fixing existing code for already
supported platform, then make it clear and we can discuss this. But if
you just want to support the bcmbca flavor, then there is no risk
mitigation involved here, and a conversion is the right step :)
I forgot to mention: the exec_op conversion is almost ready, Boris
worked on it but he lacked the hardware so maybe you'll just need to
revive the few patches which target your platform and do a little bit of
debugging?
https://github.com/bbrezillon/linux/commits/nand/exec-op-conversion?after=8a3cf6fd25d5e15c6667f9e95c1fc86e4cb735e6+34&branch=nand%2Fexec-op-conversion&qualified_name=refs%2Fheads%2Fnand%2Fexec-op-conversion
You don't need to use exec_op for your read_page/write_page hooks,
quite the opposite actually. exec_op is not meant for high throughput.
exec_op is meant to be simple. You can have fast I/Os with a different
mechanism in your read/write_page hooks.
I didn't work on open source 5 years ago. I am sorry that I missed the background of the rejected changes since then but I do not agree that this change is dirty change just because I factor out the code with is_param argument(and I offered an alternative to remove is_param with two data read functions).I actually sent out email regarding this to Boris and he cc'ed you in
sept last year. We have to use the nand parser to match the page read
from exec_op so we can actually match and use the brcmnand_page_read
fast path. But there are many situations that we need to match so the
project to migrate exce_op are still work in progress just on our
bcmbca chip as of now. Just forward that email again to you and I
appreciate it if you have any inputs there. So IMHO it is just too
risky and too big of scope to have the exec_op added to this patch
series and definitively better to do it afterwards with a dedicated
patch.
As long as you add small and orthogonal changes to cmd_ctrl/cmd_func
I don't mind, but what you want now is to force me to pull dirty
changes "first", the type of change we are refusing since 2018, making
me expect you'll perform the conversion after. It would have been
terribly less dirty and you would have all your code already upstreamed
if you had performed the exec_op conversion since September.
Thanks,
Miquèl
Attachment:
smime.p7s
Description: S/MIME Cryptographic Signature