Some questions about the spi mem framework

[Boris Brezillon]

On Thu, 17 May 2018 14:58:24 +0800
Xiangsheng Hou <xiangsheng.hou at mediatek.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 at mediatek.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 at mediatek.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.