linux-kernel - Re: [PATCH v1 0/6] PolarFire SoC Auto Update Support

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Message-ID: <cc6176cb-6792-ef11-f42a-d2d5b12d04b4@intel.com>
Date:   Mon, 27 Feb 2023 14:42:30 -0800
From:   Russ Weight <russell.h.weight@...el.com>
To:     Conor Dooley <conor@...nel.org>
CC:     Conor Dooley <conor.dooley@...rochip.com>,
        Xu Yilun <yilun.xu@...el.com>,
        Daire McNamara <daire.mcnamara@...rochip.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Moritz Fischer <mdf@...nel.org>, Wu Hao <hao.wu@...el.com>,
        Tom Rix <trix@...hat.com>, <linux-riscv@...ts.infradead.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-fpga@...r.kernel.org>
Subject: Re: [PATCH v1 0/6] PolarFire SoC Auto Update Support



On 2/27/23 14:16, Conor Dooley wrote:
> Hey Russ,
>
> On Mon, Feb 27, 2023 at 02:04:36PM -0800, Russ Weight wrote:
>> On 2/24/23 00:28, Conor Dooley wrote:
>>> On Fri, Feb 24, 2023 at 03:57:09PM +0800, Xu Yilun wrote:
>>>> On 2023-02-17 at 16:40:17 +0000, Conor Dooley wrote:
>>>>> This patchset adds support for the "Auto Update" feature on PolarFire
>>>>> SoC that allows for writing an FPGA bistream to the SPI flash connected
>>>>> to the system controller.
>>>> I haven't fully checked the patches yet, just some quick comments:
>>>>
>>>> Since this feature is just to R/W the flash, and would not affect the
>>>> runtime FPGA region, I don't think an FPGA manager is actually needed.
>>>> Why not just use the MTD uAPI? There is a set of exsiting MTD uAPI &
>>>> MTD tool if I remember correctly.
>>> A lack of interest in opening up the system controller to userspace!
>>> You're right in that the writing of the image can be done that way, and
>>> while I was testing I used the userspace bits of mtd along the way - but
>>> for validating that the image we are writing we rely on the system
>>> controller.
>>> I'm really not interested in exposing the system controller's
>>> functionality, especially the bitstream manipulation parts, to userspace
>>> due to the risk of input validation bugs, so at least that side of
>>> things should remain in the kernel.
>>> I suppose I could implement something custom in drivers/soc that does
>>> the validation only, and push the rest out to userspace. Just seemed
>>> fitting to do the whole lot in drivers/fpga.
>> In case you haven't already looked at the new firmware-upload
>> support in the firmware-loader, I'll give you some references
>> here to see if it fit you needs. This would only support the
>> write (not the read) but it would allow the controller to do
>> validation on the write.
>>
>> The is the cover letter which shows a usage example:
>> https://lore.kernel.org/lkml/20220421212204.36052-1-russell.h.weight@intel.com/
>>
>> And this is a pointer to the latest documentation for it:
>> https://docs.kernel.org/driver-api/firmware/fw_upload.html
>>
>> The only current user is: drivers/fpga/intel-m10-bmc-sec-update.c
> Sounds interesting, I shall go and take a look. Just quickly, when you
> say it wouldn't support the read, what exactly do you mean?
> The only read that I am really interested in doing is reading the first
> 1K of flash as I need to RMW it, but I don't think that that's what you
> mean.
> Do you mean that I would not be able to dump the firmware using your
> fw_upload interface? If so, that's an acceptable constraint IMO.

Yes - I mean that you couldn't dump the firmware image from userspace
using the fw_upload interface. The sysfs interface allows you to read
and write a temporary buffer, but once you "echo 0 > loading", there
is no sysfs interface associated with the firmware-loader that would
allow you to read the image from flash. Your controller actually does
the writes, so RMW in that context is fine.

- Russ
>
> Your interface also circumvents us (Microchip) defining yet another
> method for interacting with the FPGA, since from my nosing around,
> everyone seems to do something different.
>
> Cheers,
> Conor.
>