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From:   Lucas Tanure <tanure@linux.com>
Date:   Tue, 6 Aug 2019 09:02:45 +0100
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Subject: Re: Question about mfd_add_devices and platform_data
To:     linux-kernel@vger.kernel.org, Lee Jones <lee.jones@linaro.org>
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Hi Lee,

Can you help me with this question?

Thanks
Lucas

On Mon, Aug 5, 2019 at 2:43 PM Lucas Tanure <tanure@linux.com> wrote:
>
> Hi,
>
> I would like to understand mfd_add_devices call and platform_data section.
> An mfd device can have platform_data, which is kmemdup at
> platform_device_add_data from platform_device_add_data call inside
> mfd_add_device. And after this kmemdup the new mfd device receives the
> clone memory and the pointer given to platform_device_add_data is freed.
>
> All the drivers I read the platform_data is static, which in my view can
> not be freed and kfrees says:
>
> "Don't free memory not originally allocated by kmalloc() or you will run
> into trouble."
>
> So, my questions is : Should my driver kmalloc platform_data first and then
> call mfd_add_devices ? Or it's fine to give static memory to it ?
>
> Example driver:
>
> drivers/mfd/vexpress-sysreg.c:
>
> static struct syscon_platform_data vexpress_sysreg_sys_id_pdata = {
> .label = "sys_id",
> };
>
> static struct mfd_cell vexpress_sysreg_cells[] = {
> {
> .name = "syscon",
> .num_resources = 1,
> .resources = (struct resource []) {
> DEFINE_RES_MEM(SYS_ID, 0x4),
> },
> .platform_data = &vexpress_sysreg_sys_id_pdata,
> .pdata_size = sizeof(vexpress_sysreg_sys_id_pdata),
> },
>
> For this case mfd_add_devices will free vexpress_sysreg_sys_id_pdata, but
> it's static.
>
> Thanks
> Lucas