linux-kernel - Re: [PATCH V6 4/7] OF: properties: Implement get_match

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Date:   Fri, 8 Dec 2017 10:11:42 +0100
From:   Lothar Waßmann <LW@...O-electronics.de>
To:     Sinan Kaya <okaya@...eaurora.org>
Cc:     devicetree@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        timur@...eaurora.org, open list <linux-kernel@...r.kernel.org>,
        linux-acpi@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        dmaengine@...r.kernel.org, Frank Rowand <frowand.list@...il.com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH V6 4/7] OF: properties: Implement get_match_data()
 callback

Hi,

On Thu, 7 Dec 2017 12:50:50 -0500 Sinan Kaya wrote:
> On 12/7/2017 10:20 AM, Lothar Waßmann wrote:
> > Hi,
> > 
> > On Thu, 7 Dec 2017 09:45:31 -0500 Sinan Kaya wrote:
> >> On 12/7/2017 8:10 AM, Lothar Waßmann wrote:
> >>>> +void *of_fwnode_get_match_data(const struct fwnode_handle *fwnode,
> >>>> +			       struct device *dev)
> >>> Shouldn't this be 'const void *of_fwnode_get_match_data
> >>
> >> OF keeps the driver data as a (const void*) internally. ACPI keeps the
> >> driver data as kernel_ulong_t in struct acpi_device_id.
> >>
> >> I tried to find the middle ground here by converting output to void*
> >> but not keeping const.
> >>
> > It should be no problem to cast a (const void *) to an unsigned long
> > data type (without const qualifier).
> > 
> 
> It is the other way around. If I change this API to return a a (const void*),
> the device_get_match_data() function need to return a (const void *).
> 
> While implementing the ACPI piece, I have to convert an unsigned long to
> (const void *) in ACPI code so that the APIs are compatible.
> 
Just one more remark: Do you need write access to the data the pointer
returned by device_get_match_data() or of_fwnode_get_match_data()
points to?
If not, the return type of those functions should be 'const void *'.


Lothar Waßmann