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

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Message-ID: <Y/01B4hCOs9JPfR8@spud>
Date:   Mon, 27 Feb 2023 22:56:07 +0000
From:   Conor Dooley <conor@...nel.org>
To:     Russ Weight <russell.h.weight@...el.com>
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 Mon, Feb 27, 2023 at 02:42:30PM -0800, Russ Weight wrote:
> 
> 
> 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.

Ahh cool. I don't really care about dumping the firmware via such a
mechanism, so that sounds good to me.
I'll check out your approach, the immediate thought is that it sounds
suitable to my use case, so thanks!

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