Re: [PATCH 1/3] fpga: Add Efinix Trion & Titanium serial SPI programming driver

[Conor Dooley <conor@kernel.org>]

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On Fri, Oct 18, 2024 at 09:37:22AM +0800, Xu Yilun wrote:
> On Fri, Sep 27, 2024 at 04:14:42PM +0200, iansdannapel@gmail.com wrote:
> > From: Ian Dannapel <iansdannapel@gmail.com>
> > 
> > Add a new driver for loading binary firmware to volatile
> > configuration RAM using "SPI passive programming" on Efinix FPGAs.
> > 
> > Signed-off-by: Ian Dannapel <iansdannapel@gmail.com>
> > ---
> >  drivers/fpga/Kconfig                    |  10 ++
> >  drivers/fpga/Makefile                   |   1 +
> >  drivers/fpga/efinix-trion-spi-passive.c | 211 ++++++++++++++++++++++++
> >  3 files changed, 222 insertions(+)
> >  create mode 100644 drivers/fpga/efinix-trion-spi-passive.c
> > 
> > diff --git a/drivers/fpga/Kconfig b/drivers/fpga/Kconfig
> > index 37b35f58f0df..eb1e44c4e3e0 100644
> > --- a/drivers/fpga/Kconfig
> > +++ b/drivers/fpga/Kconfig
> > @@ -83,6 +83,16 @@ config FPGA_MGR_XILINX_SPI
> >  	  FPGA manager driver support for Xilinx FPGA configuration
> >  	  over slave serial interface.
> >  
> > +config FPGA_MGR_EFINIX_SPI
> > +	tristate "Efinix FPGA configuration over SPI passive"
> > +	depends on SPI
> > +	help
> > +	  This option enables support for the FPGA manager driver to
> > +	  configure Efinix Trion and Titanium Series FPGAs over SPI
> > +	  using passive serial mode.
> > +	  Warning: Do not activate this if there are other SPI devices
> > +	  on the same bus as it might interfere with the transmission.
> 
> Sorry, this won't work. As you can see, the conflict usage of CS causes
> several concerns. Just a text here is far from enough.
> 
> You need to actively work with SPI core/controller drivers to find a
> solution that coordinate the usage of this pin.

Why does it even impact other SPI devices on the bus? It's not /their/
CS line that is being modified here, it is the line for the FPGA's
programming interface, right?
What am I missing here that makes it any different to any other SPI
device that may need it's CS toggled?

Cheers,
Conor.

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