linux-kernel - Re: [PATCH v4 02/10] dmaengine: Actions: Add support for S700 DMA engine

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Date:   Tue, 30 Jun 2020 23:44:06 +0530
From:   Amit Tomer <amittomer25@...il.com>
To:     Vinod Koul <vkoul@...nel.org>
Cc:     Andre Przywara <andre.przywara@....com>,
        Andreas Färber <afaerber@...e.de>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        dan.j.williams@...el.com, cristian.ciocaltea@...il.com,
        dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-actions@...ts.infradead.org
Subject: Re: [PATCH v4 02/10] dmaengine: Actions: Add support for S700 DMA engine

Hi,

On Tue, Jun 30, 2020 at 7:54 PM Vinod Koul <vkoul@...nel.org> wrote:
>
> On 30-06-20, 15:17, Amit Tomer wrote:
> > Hi Vinod,
> >
> > On Mon, Jun 29, 2020 at 3:22 PM Vinod Koul <vkoul@...nel.org> wrote:
> >
> > > If you use of_device_get_match_data() you will not fall into this :)
> >
> > But again, of_device_get_match_data() returns void *, and we need
> > "uintptr_t" in order to type cast it properly (at-least without
> > warning).
>
> Not really, you can cast from void * to you own structure.. btw why do
> you need uintptr_t?

uintptr_t allows us to cast to an integer type that matches with enum
in terms of size, and
clang is happy about it (no more such warnings).

> The problem is a pointer to enum conversion :) I think the right way
> would be to do would be below
>
>         soc_type =  (enum foo)of_device_get_match_data(dev);
>
> or
>         soc_type =  (unsigned long) of_device_get_match_data(dev);
>
> which I think should be fine in gcc, but possibly give you above warning

Yeah, GCC is always fine with it.

> in clang.. but i thought that was fixed in clang https://reviews.llvm.org/D75758

Thanks for pointing this out.

To be honest, I thought clang had brought something important which is
missed by GCC (via emitting this warning)
that needed to be fixed in Kernel code.

But looking at this commit[1], feeling that CLANG people just wanted
to be compatible with GCC, and
in that situation why should one believe the clang ?

[1]: https://github.com/ClangBuiltLinux/llvm-project/commit/4fd4438882cc7f78e56e147d52d9a1f63b58ba81

Thanks
-Amit