linux-kernel - Re: [PATCH] habanalabs: Remove unused enum member DMA_SRAM_TO

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Date:   Sun, 23 Jan 2022 18:01:53 +0200
From:   Oded Gabbay <ogabbay@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Cai Huoqing <cai.huoqing@...ux.dev>, Arnd Bergmann <arnd@...db.de>,
        "Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] habanalabs: Remove unused enum member DMA_SRAM_TO_SRAM

On Sun, Jan 23, 2022 at 5:04 PM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> On Sun, Jan 23, 2022 at 04:43:15PM +0200, Oded Gabbay wrote:
> > On Tue, Jan 11, 2022 at 1:47 PM Cai Huoqing <cai.huoqing@...ux.dev> wrote:
> > >
> > > The driver don't support the SRAM-to-SRAM translation of DMA,
> > > so remove 'DMA_SRAM_TO_SRAM'.
> > >
> > > Signed-off-by: Cai Huoqing <cai.huoqing@...ux.dev>
> > > ---
> > >  drivers/misc/habanalabs/include/goya/goya_packets.h | 1 -
> > >  1 file changed, 1 deletion(-)
> > >
> > > diff --git a/drivers/misc/habanalabs/include/goya/goya_packets.h b/drivers/misc/habanalabs/include/goya/goya_packets.h
> > > index ef54bad20509..25fbebdc6143 100644
> > > --- a/drivers/misc/habanalabs/include/goya/goya_packets.h
> > > +++ b/drivers/misc/habanalabs/include/goya/goya_packets.h
> > > @@ -36,7 +36,6 @@ enum goya_dma_direction {
> > >         DMA_SRAM_TO_HOST,
> > >         DMA_DRAM_TO_HOST,
> > >         DMA_DRAM_TO_DRAM,
> > > -       DMA_SRAM_TO_SRAM,
> > >         DMA_ENUM_MAX
> > >  };
> > >
> > > --
> > > 2.25.1
> > >
> >
> > This is a general spec file in our s/w stack, and therefore a change
> > in it in the driver will cause our driver to be out of sync with our
> > user-space stack. i.e. the value of DMA_ENUM_MAX will be different in
> > the driver and in the user-space stack. I don't know if there will be
> > any consequences but I prefer not to risk it.
>
> If this is synced to userspace, shouldn't it be in a uapi file with a
> specific value associated with it?
>
> thanks,
>
> greg k-h

Yes, it was a mistake from day 1. A mistake we didn't repeat in future ASICs.
I take great care of putting anything that is synced between driver
and userspace in our uapi file.

Having said that, after almost 3 years of having this mistake, I feel
it is not too disastrous to leave it as is.
Our Goya s/w stack is pretty much stable and I don't want to make
changes without good reason.

wdyt ?

Oded