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SubjectRe: [PATCH V2 4/6] usb: ohci-platform: Add support for Broadcom STB SoC's
On 10/30/18, Alan Cooper <alcooperx@gmail.com> wrote:
>> On 10/24/18 3:11 AM, Arnd Bergmann wrote:
>>
>> On Wed, Oct 17, 2018 at 11:30 PM Al Cooper <alcooperx@gmail.com> wrote:
>>
>> Add support for Broadcom STB SoC's to the ohci platform driver.
>>
>> Signed-off-by: Al Cooper <alcooperx@gmail.com>
>> ---
>> drivers/usb/host/ohci-platform.c | 35
>> +++++++++++++++++++++++++++++------
>> include/linux/usb/ohci_pdriver.h | 1 +
>> 2 files changed, 30 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/usb/host/ohci-platform.c
> b/drivers/usb/host/ohci-platform.c
>> index 65a1c3fdc88c..363d6fa676a5 100644
>> --- a/drivers/usb/host/ohci-platform.c
>> +++ b/drivers/usb/host/ohci-platform.c
>> @@ -22,6 +22,7 @@
>> #include <linux/module.h>
>> #include <linux/err.h>
>> #include <linux/of.h>
>> +#include <linux/of_device.h>
>> #include <linux/platform_device.h>
>> #include <linux/pm_runtime.h>
>> #include <linux/reset.h>
>> @@ -99,12 +100,24 @@ static int ohci_platform_probe(struct
> platform_device *dev)
>> if (usb_disabled())
>> return -ENODEV;
>>
>> - /*
>> - * Use reasonable defaults so platforms don't have to provide
> these
>> - * with DT probing on ARM.
>> - */
>> - if (!pdata)
>> - pdata = &ohci_platform_defaults;
>> + if (!pdata) {
>> + const struct usb_ohci_pdata *match_pdata;
>> +
>> + match_pdata = of_device_get_match_data(&dev->dev);
>> + if (match_pdata) {
>> + pdata = devm_kzalloc(&dev->dev, sizeof(*pdata),
>> + GFP_KERNEL);
>> + if (!pdata)
>> + return -ENOMEM;
>> + *pdata = *match_pdata;
>>
>> It looks like you copy the const pdata to get a non-const version.
>> Have you tried
>> propagating the 'const' modifier so that users can rely on that here?
>
> The problem is that the const pdata from of_device_get_match() needs to be
> saved in device->platform_data which is not a const pointer (and can't be
> changed). How can I propagate the "const" to solve the problem?

Ah, I see your problem, and unfortunately don't have an easy answer.

You could split up the structure between a constant part and a non-constant
part, and have the latter be what gets put into the platform_data, but that
wouldn't really be much nicer than what you have here.

You could use devm_kmemdup() to save a few lines to simplify your
code without any other changes maybe, but it doesn't solve the
fact that the mismatch between platform_data being non-const and
of_match_data being const is a bit ugly.

Arnd

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