On Tue, 2021-12-28 at 09:17 +0100, Greg Kroah-Hartman wrote:

On Mon, Dec 27, 2021 at 05:43:15PM +0100, Niklas Schnelle wrote:

quoted

In the future inb() and friends will not be available when compiling
with CONFIG_HAS_IOPORT=n so we must only try to access them here if
CONFIG_DEVPORT is set which depends on HAS_IOPORT.

Co-developed-by: Arnd Bergmann <arnd@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@kernel.org>
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
---
 drivers/char/mem.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index cc296f0823bd..c1373617153f 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c

@@ -402,6 +402,7 @@ static int mmap_mem(struct file *file, struct vm_area_struct *vma)
 	return 0;
 }
 
+#ifdef CONFIG_DEVPORT
 static ssize_t read_port(struct file *file, char __user *buf,
 			 size_t count, loff_t *ppos)
 {

@@ -443,6 +444,7 @@ static ssize_t write_port(struct file *file, const char __user *buf,
 	*ppos = i;
 	return tmp-buf;
 }
+#endif
 
 static ssize_t read_null(struct file *file, char __user *buf,
 			 size_t count, loff_t *ppos)

@@ -665,12 +667,14 @@ static const struct file_operations null_fops = {
 	.splice_write	= splice_write_null,
 };
 
-static const struct file_operations __maybe_unused port_fops = {
+#ifdef CONFIG_DEVPORT
+static const struct file_operations port_fops = {
 	.llseek		= memory_lseek,
 	.read		= read_port,
 	.write		= write_port,
 	.open		= open_port,
 };
+#endif

Why is this #ifdef needed if it is already __maybe_unused?

Because read_port() calls inb() and write_port() calls outb() they
wouldn't compile once these are no longer defined. Then however the
read_port/write_port symbols in the struct initialization above
couldn't be resolved.

In looking closer, this change could be taken now as the use of this
variable already is behind this same #ifdef statement, right?

Yes

thanks,

greg k-h