linux-kernel - Re: Some questions about the spi mem framework

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Message-ID: <20180517094232.20651211@bbrezillon>
Date:   Thu, 17 May 2018 09:42:32 +0200
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     Xiangsheng Hou <xiangsheng.hou@...iatek.com>
Cc:     <linux-kernel@...r.kernel.org>,
        <linux-mediatek@...ts.infradead.org>,
        <linux-mtd@...ts.infradead.org>, <srv_heupstream@...iatek.com>,
        <guochun.mao@...iatek.com>, <benliang.zhao@...iatek.com>,
        <bayi.cheng@...iatek.com>, <dandan.he@...iatek.com>,
        <sean.wang@...iatek.com>, <ryder.lee@...iatek.com>,
        <xiaolei.li@...iatek.com>, <honghui.zhang@...iatek.com>
Subject: Re: Some questions about the spi mem framework

On Thu, 17 May 2018 15:35:04 +0800
Xiangsheng Hou <xiangsheng.hou@...iatek.com> wrote:

> On Thu, 2018-05-17 at 09:13 +0200, Boris Brezillon wrote:
> > On Thu, 17 May 2018 14:58:24 +0800
> > Xiangsheng Hou <xiangsheng.hou@...iatek.com> wrote:
> >   
> > > Hi Boris,
> > > 
> > > On Wed, 2018-05-16 at 14:42 +0200, Boris Brezillon wrote:  
> > > > On Wed, 16 May 2018 20:11:39 +0800
> > > > Xiangsheng Hou <xiangsheng.hou@...iatek.com> wrote:
> > > >     
> > > > > Hi Boris,
> > > > > 
> > > > > On Tue, 2018-05-15 at 17:25 +0200, Boris Brezillon wrote:    
> > > > > > Hi,
> > > > > > 
> > > > > > On Tue, 15 May 2018 11:43:20 +0800
> > > > > > Xiangsheng Hou <xiangsheng.hou@...iatek.com> wrote:
> > > > > >       
> > > > > > > Hello Boris,
> > > > > > > 
> > > > > > > I have seen you are working on extend the framework to generically
> > > > > > > support spi memory devices.
> > > > > > > And, I am working on upstream SPI Nand driver of Mediatek SPI NAND
> > > > > > > controller based on your branch[1].      
> > > > > > 
> > > > > > Great!
> > > > > >       
> > > > > > > I have some questions need your comment.
> > > > > > > 
> > > > > > > 1) There is a difference between different SPI NAND Flash when using the
> > > > > > > Quad SPI command,for example Macronix,Etron and GigaDevice, 
> > > > > > > Quad SPI commands require the Quad Enable bit in Status Register(B0H) to
> > > > > > > be set.
> > > > > > > However, current spi-mem framework does not have this operation,
> > > > > > > do you have a plan to support it?      
> > > > > > 
> > > > > > I added support for the QE bit in the v7 I sent just a few minutes ago
> > > > > > [1].      
> > > > > 
> > > > > Ok,I have studied v7.
> > > > >     
> > > > > >       
> > > > > > > 
> > > > > > > 2) I see that current spi-mem framework doesn't support ECC,
> > > > > > > But we need ECC, and we use Mediatek controller's HW ECC
> > > > > > > instead of spi nand on-chip ECC,
> > > > > > > maybe other companies also have this behavior,
> > > > > > > So the ECC part must be implemented in controller's driver.
> > > > > > > Will you abstract ECC interface in future?       
> > > > > > 
> > > > > > Well, I added support for on-die ECC in my v7 since all chips seem to
> > > > > > provide this feature. I was initially planning on abstracting ECC
> > > > > > engines, but I decided to go for a simpler approach and only support
> > > > > > on-die ECC. That does not mean we shouldn't work on this "ECC engine
> > > > > > abstraction", just that I wanted to get something out and didn't have
> > > > > > time to spend on this topic.
> > > > > > 
> > > > > > I'd be happy if someone else could work on that aspect though. BTW, do
> > > > > > you plan to use this engine [2], or is this yet another ECC engine?      
> > > > > 
> > > > > Yes,I plan to use this ecc engine[2].    
> > > > 
> > > > Cool. That probably means we'll have to move the driver one level up
> > > > (in drivers/mtd/nand) and work on this ECC engine interface I was
> > > > talking about.
> > > >      
> > > > > > > 3) You know, some nand controller need configure their registers when
> > > > > > > getting some information(page size, spare size) of nand flash,
> > > > > > > But the spi-mem framework doesn't has an interface for scanning NAND
> > > > > > > flash, when controller driver initialization.      
> > > > > > 
> > > > > > You seem to mix 2 different things:
> > > > > > - spi-mem: this is generic interface provided by the SPI framework to
> > > > > >   send spi_mem_op. There's nothing NOR or NAND specific in there, and
> > > > > >   I'd like it to stay like that as much as possible
> > > > > > - spinand: this the spi-mem driver that is dealing with SPI NAND
> > > > > >   devices, and this is where all the code related to SPI NAND support
> > > > > >   should end up.
> > > > > > 
> > > > > > Can you tell me exactly why your SPI controller needs such a detailed
> > > > > > description? Is it able to program/read pages or erase blocks on its
> > > > > > own? Do you have a spec of this controller publicly available?      
> > > > > 
> > > > > For Mediatek SPI Nand controller,I have to configure registers for ECC
> > > > > engine,page format and spare format according to nand information just
> > > > > like[3] in mtk_nfc_hw_runtime_config() function.    
> > > > 
> > > > So it's all related to the NAND controller, nothing specific to the SPI
> > > > controller, right?    
> > > 
> > > Yes,we use NAND controller rather than SPI controller.  
> > 
> > Sorry, I meant ECC engine, not NAND controller.  
> 
> It's related to ECC engine and NAND controller.

Not sure I understand what you call NAND controller. Is it a SPI NAND
controller or the raw NAND controller available in
drivers/mtd/nand/raw? And if it's a SPI NAND controller, does that mean
MTK implements a NAND dedicated logic on top of its SPI controller?