Re: [v3 4/4] spi: aspeed: Add ASPEED FMC/SPI memory controller driver

[Boris Brezillon]

On Fri, 6 Nov 2020 08:58:23 +0000
Chin-Ting Kuo <chin-ting_kuo@xxxxxxxxxxxxxx> wrote:

> Hi Boris,
> 
> Thanks for your quick reply.
> 
> > -----Original Message-----
> > From: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
> > Sent: Thursday, November 5, 2020 11:12 PM
> > To: Cédric Le Goater <clg@xxxxxxxx>; robh+dt@xxxxxxxxxx
> > Cc: Chin-Ting Kuo <chin-ting_kuo@xxxxxxxxxxxxxx>; broonie@xxxxxxxxxx;
> > joel@xxxxxxxxx; andrew@xxxxxxxx; bbrezillon@xxxxxxxxxx;
> > devicetree@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> > linux-aspeed@xxxxxxxxxxxxxxxx; linux-spi@xxxxxxxxxxxxxxx; BMC-SW
> > <BMC-SW@xxxxxxxxxxxxxx>
> > Subject: Re: [v3 4/4] spi: aspeed: Add ASPEED FMC/SPI memory controller
> > driver
> > 
> > Hi,
> > 
> > On Thu, 5 Nov 2020 15:09:11 +0100
> > Cédric Le Goater <clg@xxxxxxxx> wrote:
> >   
> > > Hello Chin-Ting,
> > >
> > > Thanks for this driver. It's much cleaner than the previous and we
> > > should try adding support for the AST2500 SoC also. I guess we can
> > > keep the old driver for the AST2400 which has a different register layout.
> > >
> > > On the patchset, I think we should split this patch in three :
> > >
> > >  - basic support
> > >  - AHB window calculation depending on the flash size
> > >  - read training support  
> > 
> > I didn't look closely at the implementation, but if the read training tries to read
> > a section of the NOR, I'd recommend exposing that feature through spi-mem
> > and letting the SPI-NOR framework trigger the training instead of doing that at
> > dirmap creation time (remember that spi-mem is also used for SPI NANDs
> > which use the dirmap API too, and this training is unlikely to work there).
> > 
> > The SPI-NOR framework could pass a read op template and a reference pattern
> > such that all the spi-mem driver has to do is execute the template op and
> > compare the output to the reference buffer.
> >   
> 
> I agree it. Before, I were not able to find a suitable location to implement read training feature.
> I think that I can add a SPI timing training function in "spi_controller_mem_ops" struct and
> call it by a wrapper function called at the bottom of spi_nor_probe() in spi-nor.c.
> Maybe, SPI-NOR framework does not need to pass reference buffer since calibration
> method depends on each SoC itself and buffer size may be variant.
> The detail calibration method may be implemented in each SoC SPI driver.

That's a real problem IMO. What makes this pattern SoC specific? I can
see why the location in flash could be *board* specific, but the
pattern should be pretty common, right? As for the spi-mem operation to
be executed, it's definitely memory specific (I can imagine some flash
vendors providing a specific command returning a fixed pattern that's
not actually stored on a visible portion of the flash).

> 
> Besides, I am thinking about the possibility for adding a "spi_mem_post_init" function in
> spi-mem framework sine for some SoCs, SPI controller needs to adjust some settings
> after getting SPI flash information.

I don't think that's a good idea. The spi-mem interface should stay
memory-type agnostic and doing that means we somehow pass NOR specific
info. What is it that you need exactly, and why?