Re: [RFC v1 0/3] *spi-mem: adding setup and callback function

[Boris Brezillon <boris.brezillon@collabora.com>]

Trimmed the recipient list a bit and used Frieder's new address.
+Sergey

On Mon, 29 Jul 2019 23:55:05 +0300
Tomer Maimon <tmaimon77@gmail.com> wrote:

> Hi Boris,
> 
> Thanks for the prompt reply,
> 
> 
> 
> On Mon, 29 Jul 2019 at 18:29, Boris Brezillon <boris.brezillon@collabora.com>
> wrote:
> 
> > Hi Tomer,
> >
> > On Mon, 29 Jul 2019 17:25:01 +0300
> > Tomer Maimon <tmaimon77@gmail.com> wrote:
> >  
> > > Lately we have working on Flash interface unit (FIU) SPI driver that
> > > using spi-mem interface, Our FIU HW module support direct Flash Rd//Wr.
> > >
> > > In our SOC (32 bit dual core ARM) we have 3 FIU's that using memory  
> > mapping as follow:  
> > >
> > > FIU0 - have 2 chip select and each one have 128MB memory mapping (total  
> > 256MB memory mapping)  
> > > FIU1 - have 4 chip select and each one have 128MB memory mapping (total  
> > 512MB memory mapping)  
> > > FIU2 - have 4 chip select and each one have 16MB memory mapping (total  
> > 32MB memory mapping)  
> > >
> > > Totally 800MB memory mapping.
> > >
> > > When the FIU driver probe it don't know the size of each Flash that
> > > connected to the FIU, so the entire memory mapping is allocated for each  
> > FIU  
> > > according the FIU device tree memory map parameters.  
> >
> > Do you need those mappings to be active to support simple reg accesses?
> >  
> > > It means, if we enable all three FIU's the drivers will try to allocate  
> > totally 800MB.  
> > >
> > > In 32bit system it is problematic because the kernel have only 1GB
> > > of memory allocation so the vmalloc cannot take 800MB.
> > >
> > > When implementing the FIU driver in the mtd/spi-nor we allocating memory  
> > address only  
> > > for detected Flash with exact size (usually we are not using 128MB  
> > Flash), and in that case usually we allocating much less memory.  
> > >
> > > To solve this issue we needed to overcome two things:
> > >
> > > 1.    Get argument from the upper layer (spi-mem layer)
> > > 2.    Calling the get argument function after SPI_NOR_SCAN function.  
> > (the MTD Flash size filled in  SPI_NOR_SCAN function)
> >
> > That's clearly breaking the layering we've tried to restore with the
> > spi-nor/spi-mem split, and I don't see why this is needed since we now
> > have a way to create direct mappings dynamically (with the dirmap API).
> > Have you tried implementing the dirmap hooks in your driver?  
> 
> 
>  Sorry but I wasn't familiar with the direct mapping in the spi-mem, it
> seems it needed to implemented in the m25p80 driver as well, am I correct?

There's this patch [1] floating around. IIRC, Sergey was waiting for
the m25p80 -> spi-nor merge to send a v5. Vignesh, any updates on that
one? If you don't have time to work on that, maybe Sergey could send a
v5.

[1]https://www.spinics.net/lists/linux-mtd/msg07358.html

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