[PATCH 2/5] mtd: rawnand: qcom: Add initial support for qspi nand

[Miquel Raynal]

Hello,

+ Mark

quic_mdalam at quicinc.com wrote on Mon, 27 Mar 2023 19:24:02 +0530:

> On 3/6/2023 8:08 PM, Miquel Raynal wrote:
> > Hello,
> > 
> > quic_mdalam at quicinc.com wrote on Mon, 6 Mar 2023 19:45:58 +0530:
> >   
> >> On 10/29/2020 2:37 PM, Boris Brezillon wrote:  
> >>> Hello,
> >>>
> >>> On Sat, 10 Oct 2020 11:01:39 +0530
> >>> Md Sadre Alam <mdalam at codeaurora.org> wrote:  
> >>>   >>>> This change will add initial support for qspi (serial nand).  
> >>>>
> >>>> QPIC Version v.2.0 onwards supports serial nand as well so this
> >>>> change will initialize all required register to enable qspi (serial
> >>>> nand).
> >>>>
> >>>> This change is supporting very basic functionality of qspi nand flash.
> >>>>
> >>>> 1. Reset device (Reset QSPI NAND device).
> >>>>
> >>>> 2. Device detection (Read id QSPI NAND device).  
> >>> Unfortunately, that's not going to work in the long term. You're
> >>> basically hacking the raw NAND framework to make SPI NANDs fit. I do
> >>> understand the rationale behind this decision (re-using the code for
> >>> ECC and probably other things), but that's not going to work. So I'd
> >>> recommend doing the following instead:
> >>>
> >>> 1/ implement a SPI-mem controller driver
> >>> 2/ implement an ECC engine driver so the ECC logic can be shared
> >>>      between the SPI controller and raw NAND controller drivers
> >>> 3/ convert the raw NAND driver to the exec_op() interface (none of
> >>>      this hack would have been possible if the driver was using the new
> >>>      API)
> >>>
> >>> Regards,
> >>>
> >>> Boris  
> >>>   >>      Sorry for late reply, again started working on this feature support.  The QPIC v2 on wards there is serial nand support got added , its not a standard SPI controller  
> >>
> >>      its QPIC controller having support for serial nand. All SPI related configuration done by QPIC hardware and its not exposed as SPI bus to the external world. Only based on
> >>
> >>      QPIC_SPI_CFG = 1, serial functionality will get selected. So that no need to implement as SPI-mem controller driver, since its not a SPI controller.
> >>
> >>     Please check the below diagram for top view of QPIC controller.  
> > 
> > One of the hard things in the Linux kernel is to make devices fit
> > frameworks. This feature does not fit the raw NAND framework. It does
> > not follow any of the conventions taken there. It is not gonna be
> > accepted there. You need to expose spi-mem functionalities, even if the
> > spi-proper features are not available. I believe your situation still
> > fits the spi-mem abstraction.
> > 
> > Thanks,
> > Miquèl  
> 
> 
> I have started writing the driver code for SPI NAND. Please check the below design,
> is this fine as per Boris suggestion.

Thanks.


>            |------------------------|                      |------------------------------|                        |---------------------------------|
>            |qcom spi nand driver    |--------------------->|common ECC engine driver      |<-----------------------|qcom raw nand driver             |
>            |                        |                      |                              |                        |                                 |
>            |                        |                      |drivers/mtd/nand/ecc-qcom.c   |                        |drivers/mtd/nand/raw/qcom_nand.c |
>            |                        |                      |                              |                        |                                 |
>            |drivers/spi/spi-qpic.c  |                      |------------------------------|                        |                                 |
>            |                        |                      |common API file:              |                        |                                 |
>            |                        |                      |common API: reset, read id,   |                        |                                 |
>            |                        |--------------------->|erase, read page, write page, |<-----------------------|                                 |
>            |------------------------|                      |bad block check etc.          |                        |                                 |
>                                                            |                              |                        |---------------------------------|
>                                                            |drivers/mtd/nand/raw/qpic_comm|
>                                                            |    on.c                      |
>                                                            |------------------------------|
> 
> 
> Here ECC engine driver as separate file under (drivers/mtd/nand/ecc-qcom.c) and all
> common APIs like reset, read id, erase, write page, read page, check block bad etc.

I'm not sure how generic these APIs are, please try to not put anything
raw NAND or SPI-NAND specific in the common file. I don't want to see
"if (raw)" or "if (spi)" conditions there.

> as separate file under drivers/mtd/nand/raw/qpic_common.c.APIs under ECC engine drivers
> and qpic_common.c will be exported and used by spi-qpic.c driver (Serial NAND) and qcom_nand.c
> (raw nand driver).

On my side, I don't have a strong opinion yet but it looks good to me.

Can you confirm you are considering switching to the ->exec_op() API in
the raw NAND driver?

Thanks,
Miquèl