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From:   Lucas Tanure <tanure@linux.com>
Date:   Mon, 5 Aug 2019 14:43:53 +0100
Message-ID: <CAJX_Q+21M+W6B2Ab9TZeNSSCVdLcU1J1LBCHO13CR0T+e=SVOQ@mail.gmail.com>
Subject: Question about mfd_add_devices and platform_data
To:     linux-kernel@vger.kernel.org
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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