[PATCH 3/4] mtd/fpga: add fpga directory to mtd (with Cyclone 10)

[Ulf Samuelsson]

On 2023-02-22 20:51, Steffen Dirkwinkel wrote:
> Hi!
> 
> On Tue, 2023-02-21 at 11:58 +0100, Ulf Samuelsson wrote:
>> CAUTION: External Email!!
>> Hi Guys,
>> We are currently discussing how to support passive serial configuration
>> of FPGAs in u-boot.
>>
>> Checking the u-boot source code reveals that only your boards
>> actually supports this.
>>
>> board/beckhoff/mx53cx9020/mx53cx9020.c:...Altera_CYC2_Passive_Serial ...
>> $ scripts/get_maintainer.pl board/beckhoff/mx53cx9020/mx53cx9020.c
>> Patrick Bruenn <p.bruenn at beckhoff.com> (maintainer:MX53 CX9020)
> 
> This doesn't seem immediately relevant to our board as we don't really use spi,
> but the (w)eim interface as far as i can tell right now. (has been a while since I looked
> at it, have not read the imx datasheet again to see if this is spi in disguise)
> 
> If anything the binding should be shared between u-boot and the kernel. We just had a bug
> because of differences between the two.
> Something like the "altr,fpga-passive-serial" in arch/arm/boot/dts/imx6q-evi.dts in the kernel would match the
> usecase.
> 
> We wouldn't be opposed to changing the dt and also just repaired our CI for these devices and can test changes quickly.
> 
I had a look at your code again.
It appears that you are using the Altera "passive serial" interface in 
U-Boot, but your board routine appears to write 8-bit bytes to the 
external bus.

The only two reasons for this I can think of is that you are either
using an external serializer converting the 8 bit words to
a serial stream or you are actually using the passive "parallell
interface" on the FPGA, but use the "passive serial" routines
in u-boot.

Can you please confirm how the hardware works?


The maintainer of the other board using "passive serial" 
(w.wegner at astro-kom.de <w.wegner at astro-kom.de>)
bounced as an unknown user.  This means that the "board/astro/mcf5373" 
does not have an active MAINTAINER.

The board was added in 2010, and has not seen any updates from
astro-kom.de since then. All the maintenance has been by people 
maintaining subsystems.

Best Regards
Ulf Samuelsson


> Best Regards
> Steffen Dirkwinkel
> 
>>
>> board/astro/mcf5373l/fpga.c:Altera_CYC2_Passive_Serial ...
>> $ scripts/get_maintainer.pl board/astro/mcf5373l/fpga.c
>> Wolfgang Wegner <w.wegner at astro-kom.de> (maintainer:MCF5373L BOARD)
>>
>> The proposed ideas is to have the FPGA as an SPI peripheral
>> in the device tree.
>>
>> I have a working version, where the FPGA is an MTD device
>> and the general idea is to add it to the FPGA manager,
>> which unfortunately needs a major rewrite to support device tree.
>>
>> Your board support configuring the FPGA in the 'board' files.
>>
>>
>> * Are these boards still active and will require updates of u-boot?
>>
>> * If so, would it be a problem porting the FPGA configuration to the
>> device tree?
>>
>> Marek does not want two drivers supporting passive serial,
>> and supporting both 'board' drivers and devicetree drivers
>> seems to result in unclean code.
>>
>> Best Regards
>> Ulf Samuelsson
> 
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