diff mbox series

[3/3] serial: Add kserial_rs485 to avoid wasted space due to .padding

Message ID 20220826144629.11507-4-ilpo.jarvinen@linux.intel.com (mailing list archive)
State New, archived
Headers show
Series None | expand

Commit Message

Ilpo Järvinen Aug. 26, 2022, 2:46 p.m. UTC 
Struct serial_rs485 has a .padding field to make uapi updates easier.
It wastes space, however. Create struct kserial_rs485 which is a kerner
counterpart w/o padding.

kernel_serial_rs485_to_user_rs485()'s rs485 can now become const as
padding is dealt within the local variable.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
---
 .../driver-api/serial/serial-rs485.rst        |  2 +-
 drivers/tty/serial/8250/8250.h                |  4 +-
 drivers/tty/serial/8250/8250_dwlib.c          |  6 +--
 drivers/tty/serial/8250/8250_exar.c           | 12 ++---
 drivers/tty/serial/8250/8250_fintek.c         |  6 +--
 drivers/tty/serial/8250/8250_lpc18xx.c        |  4 +-
 drivers/tty/serial/8250/8250_pci.c            |  4 +-
 drivers/tty/serial/8250/8250_port.c           |  4 +-
 drivers/tty/serial/amba-pl011.c               |  4 +-
 drivers/tty/serial/ar933x_uart.c              |  8 ++--
 drivers/tty/serial/atmel_serial.c             |  4 +-
 drivers/tty/serial/fsl_lpuart.c               |  6 +--
 drivers/tty/serial/imx.c                      |  6 +--
 drivers/tty/serial/max310x.c                  |  4 +-
 drivers/tty/serial/mcf.c                      |  4 +-
 drivers/tty/serial/omap-serial.c              |  6 +--
 drivers/tty/serial/sc16is7xx.c                |  6 +--
 drivers/tty/serial/serial_core.c              | 48 +++++++++++++------
 drivers/tty/serial/stm32-usart.c              | 12 ++---
 include/linux/serial_core.h                   | 20 ++++++--
 include/uapi/linux/serial.h                   |  3 +-
 21 files changed, 104 insertions(+), 69 deletions(-)

Comments

Andy Shevchenko Aug. 26, 2022, 3:50 p.m. UTC | #1 
On Fri, Aug 26, 2022 at 5:51 PM Ilpo Järvinen
<ilpo.jarvinen@linux.intel.com> wrote:
>
> Struct serial_rs485 has a .padding field to make uapi updates easier.

The struct

> It wastes space, however. Create struct kserial_rs485 which is a kerner
> counterpart w/o padding.
>
> kernel_serial_rs485_to_user_rs485()'s rs485 can now become const as
> padding is dealt within the local variable.

...

> -static int user_rs485_to_kernel_serial_rs485(struct serial_rs485 *rs485,
> +static int user_rs485_to_kernel_serial_rs485(struct kserial_rs485 *rs485,
>                                              const struct serial_rs485 __user *rs485_user)
>  {
> -       if (copy_from_user(rs485, rs485_user, sizeof(*rs485)))
> +       struct serial_rs485 rs485_uapi;
> +
> +       if (copy_from_user(&rs485_uapi, rs485_user, sizeof(*rs485)))
>                 return -EFAULT;

> +       *rs485 = *((struct kserial_rs485 *)&rs485_uapi);

So with all assets we have we can be sure that on BE64 / BE32 machines
this will be flawless. Is this assumption correct?

>         return 0;
>  }

...

>  static int kernel_serial_rs485_to_user_rs485(struct serial_rs485 __user *rs485_user,
> -                                            struct serial_rs485 *rs485)
> +                                            const struct kserial_rs485 *rs485)
>  {
> +       struct serial_rs485 rs485_uapi;

> +       *((struct kserial_rs485 *)&rs485_uapi) = *rs485;

Ditto.

+ Blank line?

>         /* Return clean padding area to userspace */
> -       memset(rs485->padding0, 0, sizeof(rs485->padding0));
> -       memset(rs485->padding1, 0, sizeof(rs485->padding1));
> +       memset(rs485_uapi.padding0, 0, sizeof(rs485_uapi.padding0));
> +       memset(rs485_uapi.padding1, 0, sizeof(rs485_uapi.padding1));
>
> -       if (copy_to_user(rs485_user, rs485, sizeof(*rs485)))
> +       if (copy_to_user(rs485_user, &rs485_uapi, sizeof(rs485_uapi)))
>                 return -EFAULT;
>
>         return 0;

...

> +/* Compile-time asserts for kserial_rs485 and serial_rs485 equality (except padding) */

struct kserial_rs485
struct serial_rs485

(rationale: standard representation in text / comments and be a link
in case if this is converted to kernel doc)

...

> +/*
> + * Must match with serial_rs485 in include/uapi/linux/serial.h excluding the

Ditto.

> + * padding.
> + */
> +struct kserial_rs485 {
> +       __u32   flags;                  /* RS485 feature flags */
> +       __u32   delay_rts_before_send;  /* Delay before send (milliseconds) */
> +       __u32   delay_rts_after_send;   /* Delay after send (milliseconds) */
> +       struct {
> +               __u8    addr_recv;
> +               __u8    addr_dest;
> +       };

Btw, can't we convert them to kernel doc?

> +};

...

> + * There's kernel counterpart kserial_rs485 of this struct without padding.

struct kserial_rs485
Ilpo Järvinen Aug. 29, 2022, 12:09 p.m. UTC | #2 
On Fri, 26 Aug 2022, Andy Shevchenko wrote:

> On Fri, Aug 26, 2022 at 5:51 PM Ilpo Järvinen
> <ilpo.jarvinen@linux.intel.com> wrote:
> 
> > -static int user_rs485_to_kernel_serial_rs485(struct serial_rs485 *rs485,
> > +static int user_rs485_to_kernel_serial_rs485(struct kserial_rs485 *rs485,
> >                                              const struct serial_rs485 __user *rs485_user)
> >  {
> > -       if (copy_from_user(rs485, rs485_user, sizeof(*rs485)))
> > +       struct serial_rs485 rs485_uapi;
> > +
> > +       if (copy_from_user(&rs485_uapi, rs485_user, sizeof(*rs485)))
> >                 return -EFAULT;
> 
> > +       *rs485 = *((struct kserial_rs485 *)&rs485_uapi);
> 
> So with all assets we have we can be sure that on BE64 / BE32 machines
> this will be flawless. Is this assumption correct?

I think so. At worst it could trigger a build fail assuming the kernel 
would do some really odd struct layout reordering (which, according to 
the build bot, doesn't occur for any currently tested arch).

Now that you highlighted this line though, I started to wonder if it would 
be just better to use memcpy() instead as it would avoid those casts.

> > + * padding.
> > + */
> > +struct kserial_rs485 {
> > +       __u32   flags;                  /* RS485 feature flags */
> > +       __u32   delay_rts_before_send;  /* Delay before send (milliseconds) */
> > +       __u32   delay_rts_after_send;   /* Delay after send (milliseconds) */
> > +       struct {
> > +               __u8    addr_recv;
> > +               __u8    addr_dest;
> > +       };
> 
> Btw, can't we convert them to kernel doc?

Yes, why not.
Andy Shevchenko Aug. 29, 2022, 12:14 p.m. UTC | #3 
On Mon, Aug 29, 2022 at 3:09 PM Ilpo Järvinen
<ilpo.jarvinen@linux.intel.com> wrote:
> On Fri, 26 Aug 2022, Andy Shevchenko wrote:
> > On Fri, Aug 26, 2022 at 5:51 PM Ilpo Järvinen
> > <ilpo.jarvinen@linux.intel.com> wrote:

...

> > > +       *rs485 = *((struct kserial_rs485 *)&rs485_uapi);
> >
> > So with all assets we have we can be sure that on BE64 / BE32 machines
> > this will be flawless. Is this assumption correct?
>
> I think so. At worst it could trigger a build fail assuming the kernel
> would do some really odd struct layout reordering (which, according to
> the build bot, doesn't occur for any currently tested arch).
>
> Now that you highlighted this line though, I started to wonder if it would
> be just better to use memcpy() instead as it would avoid those casts.

Actually the current version might be better since the compiler will
be aware of the types, but it still requires a proper layout of the
fields. That said, I leave it for you.
diff mbox series

Patch

diff --git a/Documentation/driver-api/serial/serial-rs485.rst b/Documentation/driver-api/serial/serial-rs485.rst
index 6ebad75c74ed..7e496336a01b 100644
--- a/Documentation/driver-api/serial/serial-rs485.rst
+++ b/Documentation/driver-api/serial/serial-rs485.rst
@@ -41,7 +41,7 @@  RS485 Serial Communications
    implement the rs485_config callback and provide rs485_supported in the
    uart_port structure. The serial core calls rs485_config to do the device
    specific part in response to TIOCSRS485 ioctl (see below). The rs485_config
-   callback receives a pointer to a sanitizated serial_rs485 structure. The
+   callback receives a pointer to a sanitizated kserial_rs485 structure. The
    serial_rs485 userspace provides is sanitized before calling rs485_config
    using rs485_supported that indicates what RS485 features the driver supports
    for the uart_port. TIOCGRS485 ioctl can be used to read back the
diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
index 287153d32536..4e22f8d50e91 100644
--- a/drivers/tty/serial/8250/8250.h
+++ b/drivers/tty/serial/8250/8250.h
@@ -204,11 +204,11 @@  void serial8250_rpm_get_tx(struct uart_8250_port *p);
 void serial8250_rpm_put_tx(struct uart_8250_port *p);
 
 int serial8250_em485_config(struct uart_port *port, struct ktermios *termios,
-			    struct serial_rs485 *rs485);
+			    struct kserial_rs485 *rs485);
 void serial8250_em485_start_tx(struct uart_8250_port *p);
 void serial8250_em485_stop_tx(struct uart_8250_port *p);
 void serial8250_em485_destroy(struct uart_8250_port *p);
-extern struct serial_rs485 serial8250_em485_supported;
+extern struct kserial_rs485 serial8250_em485_supported;
 
 /* MCR <-> TIOCM conversion */
 static inline int serial8250_TIOCM_to_MCR(int tiocm)
diff --git a/drivers/tty/serial/8250/8250_dwlib.c b/drivers/tty/serial/8250/8250_dwlib.c
index dbe4d44f60d4..a628ed2c235b 100644
--- a/drivers/tty/serial/8250/8250_dwlib.c
+++ b/drivers/tty/serial/8250/8250_dwlib.c
@@ -134,7 +134,7 @@  static void dw8250_update_rar(struct uart_port *p, u32 addr)
 		dw8250_writel_ext(p, DW_UART_RE_EN, re_en);
 }
 
-static void dw8250_rs485_set_addr(struct uart_port *p, struct serial_rs485 *rs485,
+static void dw8250_rs485_set_addr(struct uart_port *p, struct kserial_rs485 *rs485,
 				  struct ktermios *termios)
 {
 	u32 lcr = dw8250_readl_ext(p, DW_UART_LCR_EXT);
@@ -177,7 +177,7 @@  static void dw8250_rs485_set_addr(struct uart_port *p, struct serial_rs485 *rs48
 }
 
 static int dw8250_rs485_config(struct uart_port *p, struct ktermios *termios,
-			       struct serial_rs485 *rs485)
+			       struct kserial_rs485 *rs485)
 {
 	u32 tcr;
 
@@ -232,7 +232,7 @@  static bool dw8250_detect_rs485_hw(struct uart_port *p)
 	return reg;
 }
 
-static const struct serial_rs485 dw8250_rs485_supported = {
+static const struct kserial_rs485 dw8250_rs485_supported = {
 	.flags = SER_RS485_ENABLED | SER_RS485_RX_DURING_TX | SER_RS485_RTS_ON_SEND |
 		 SER_RS485_RTS_AFTER_SEND | SER_RS485_ADDRB | SER_RS485_ADDR_RECV |
 		 SER_RS485_ADDR_DEST,
diff --git a/drivers/tty/serial/8250/8250_exar.c b/drivers/tty/serial/8250/8250_exar.c
index 314a05e009df..9fef2056a9b5 100644
--- a/drivers/tty/serial/8250/8250_exar.c
+++ b/drivers/tty/serial/8250/8250_exar.c
@@ -113,8 +113,8 @@  struct exar8250;
 
 struct exar8250_platform {
 	int (*rs485_config)(struct uart_port *port, struct ktermios *termios,
-			    struct serial_rs485 *rs485);
-	const struct serial_rs485 *rs485_supported;
+			    struct kserial_rs485 *rs485);
+	const struct kserial_rs485 *rs485_supported;
 	int (*register_gpio)(struct pci_dev *, struct uart_8250_port *);
 	void (*unregister_gpio)(struct uart_8250_port *);
 };
@@ -411,7 +411,7 @@  static void xr17v35x_unregister_gpio(struct uart_8250_port *port)
 }
 
 static int generic_rs485_config(struct uart_port *port, struct ktermios *termios,
-				struct serial_rs485 *rs485)
+				struct kserial_rs485 *rs485)
 {
 	bool is_rs485 = !!(rs485->flags & SER_RS485_ENABLED);
 	u8 __iomem *p = port->membase;
@@ -431,7 +431,7 @@  static int generic_rs485_config(struct uart_port *port, struct ktermios *termios
 	return 0;
 }
 
-static const struct serial_rs485 generic_rs485_supported = {
+static const struct kserial_rs485 generic_rs485_supported = {
 	.flags = SER_RS485_ENABLED,
 };
 
@@ -443,7 +443,7 @@  static const struct exar8250_platform exar8250_default_platform = {
 };
 
 static int iot2040_rs485_config(struct uart_port *port, struct ktermios *termios,
-				struct serial_rs485 *rs485)
+				struct kserial_rs485 *rs485)
 {
 	bool is_rs485 = !!(rs485->flags & SER_RS485_ENABLED);
 	u8 __iomem *p = port->membase;
@@ -475,7 +475,7 @@  static int iot2040_rs485_config(struct uart_port *port, struct ktermios *termios
 	return generic_rs485_config(port, termios, rs485);
 }
 
-static const struct serial_rs485 iot2040_rs485_supported = {
+static const struct kserial_rs485 iot2040_rs485_supported = {
 	.flags = SER_RS485_ENABLED | SER_RS485_RX_DURING_TX | SER_RS485_TERMINATE_BUS,
 };
 
diff --git a/drivers/tty/serial/8250/8250_fintek.c b/drivers/tty/serial/8250/8250_fintek.c
index 65b6b3cbaff6..d3d2e25dd06b 100644
--- a/drivers/tty/serial/8250/8250_fintek.c
+++ b/drivers/tty/serial/8250/8250_fintek.c
@@ -192,7 +192,7 @@  static int fintek_8250_get_ldn_range(struct fintek_8250 *pdata, int *min,
 }
 
 static int fintek_8250_rs485_config(struct uart_port *port, struct ktermios *termios,
-			      struct serial_rs485 *rs485)
+			      struct kserial_rs485 *rs485)
 {
 	uint8_t config = 0;
 	struct fintek_8250 *pdata = port->private_data;
@@ -411,13 +411,13 @@  static int probe_setup_port(struct fintek_8250 *pdata,
 }
 
 /* Only the first port supports delays */
-static const struct serial_rs485 fintek_8250_rs485_supported_port0 = {
+static const struct kserial_rs485 fintek_8250_rs485_supported_port0 = {
 	.flags = SER_RS485_ENABLED | SER_RS485_RTS_ON_SEND | SER_RS485_RTS_AFTER_SEND,
 	.delay_rts_before_send = 1,
 	.delay_rts_after_send = 1,
 };
 
-static const struct serial_rs485 fintek_8250_rs485_supported = {
+static const struct kserial_rs485 fintek_8250_rs485_supported = {
 	.flags = SER_RS485_ENABLED | SER_RS485_RTS_ON_SEND | SER_RS485_RTS_AFTER_SEND,
 };
 
diff --git a/drivers/tty/serial/8250/8250_lpc18xx.c b/drivers/tty/serial/8250/8250_lpc18xx.c
index 6dc85aaba5d0..0619427683cf 100644
--- a/drivers/tty/serial/8250/8250_lpc18xx.c
+++ b/drivers/tty/serial/8250/8250_lpc18xx.c
@@ -33,7 +33,7 @@  struct lpc18xx_uart_data {
 };
 
 static int lpc18xx_rs485_config(struct uart_port *port, struct ktermios *termios,
-				struct serial_rs485 *rs485)
+				struct kserial_rs485 *rs485)
 {
 	struct uart_8250_port *up = up_to_u8250p(port);
 	u32 rs485_ctrl_reg = 0;
@@ -81,7 +81,7 @@  static void lpc18xx_uart_serial_out(struct uart_port *p, int offset, int value)
 	writel(value, p->membase + offset);
 }
 
-static const struct serial_rs485 lpc18xx_rs485_supported = {
+static const struct kserial_rs485 lpc18xx_rs485_supported = {
 	.flags = SER_RS485_ENABLED | SER_RS485_RTS_ON_SEND | SER_RS485_RTS_AFTER_SEND,
 	.delay_rts_after_send = 1,
 	/* Delay RTS before send is not supported */
diff --git a/drivers/tty/serial/8250/8250_pci.c b/drivers/tty/serial/8250/8250_pci.c
index 6f66dc2ebacc..8675b0d9658d 100644
--- a/drivers/tty/serial/8250/8250_pci.c
+++ b/drivers/tty/serial/8250/8250_pci.c
@@ -1554,7 +1554,7 @@  pci_brcm_trumanage_setup(struct serial_private *priv,
 
 /* We should do proper H/W transceiver setting before change to RS485 mode */
 static int pci_fintek_rs485_config(struct uart_port *port, struct ktermios *termios,
-			       struct serial_rs485 *rs485)
+			       struct kserial_rs485 *rs485)
 {
 	struct pci_dev *pci_dev = to_pci_dev(port->dev);
 	u8 setting;
@@ -1583,7 +1583,7 @@  static int pci_fintek_rs485_config(struct uart_port *port, struct ktermios *term
 	return 0;
 }
 
-static const struct serial_rs485 pci_fintek_rs485_supported = {
+static const struct kserial_rs485 pci_fintek_rs485_supported = {
 	.flags = SER_RS485_ENABLED | SER_RS485_RTS_ON_SEND,
 	/* F81504/508/512 does not support RTS delay before or after send */
 };
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 39b35a61958c..2345b6fbac6d 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -647,7 +647,7 @@  void serial8250_em485_destroy(struct uart_8250_port *p)
 }
 EXPORT_SYMBOL_GPL(serial8250_em485_destroy);
 
-struct serial_rs485 serial8250_em485_supported = {
+struct kserial_rs485 serial8250_em485_supported = {
 	.flags = SER_RS485_ENABLED | SER_RS485_RTS_ON_SEND | SER_RS485_RTS_AFTER_SEND |
 		 SER_RS485_TERMINATE_BUS | SER_RS485_RX_DURING_TX,
 	.delay_rts_before_send = 1,
@@ -665,7 +665,7 @@  EXPORT_SYMBOL_GPL(serial8250_em485_supported);
  * hardware, relying on software emulation instead.
  */
 int serial8250_em485_config(struct uart_port *port, struct ktermios *termios,
-			    struct serial_rs485 *rs485)
+			    struct kserial_rs485 *rs485)
 {
 	struct uart_8250_port *up = up_to_u8250p(port);
 
diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index 15f0e4d88c5a..e78cd0759dc1 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -2215,7 +2215,7 @@  static int pl011_verify_port(struct uart_port *port, struct serial_struct *ser)
 }
 
 static int pl011_rs485_config(struct uart_port *port, struct ktermios *termios,
-			      struct serial_rs485 *rs485)
+			      struct kserial_rs485 *rs485)
 {
 	struct uart_amba_port *uap =
 		container_of(port, struct uart_amba_port, port);
@@ -2765,7 +2765,7 @@  static int pl011_register_port(struct uart_amba_port *uap)
 	return ret;
 }
 
-static const struct serial_rs485 pl011_rs485_supported = {
+static const struct kserial_rs485 pl011_rs485_supported = {
 	.flags = SER_RS485_ENABLED | SER_RS485_RTS_ON_SEND | SER_RS485_RTS_AFTER_SEND |
 		 SER_RS485_RX_DURING_TX,
 	.delay_rts_before_send = 1,
diff --git a/drivers/tty/serial/ar933x_uart.c b/drivers/tty/serial/ar933x_uart.c
index 32caeac12985..30c716b4a105 100644
--- a/drivers/tty/serial/ar933x_uart.c
+++ b/drivers/tty/serial/ar933x_uart.c
@@ -391,7 +391,7 @@  static void ar933x_uart_rx_chars(struct ar933x_uart_port *up)
 static void ar933x_uart_tx_chars(struct ar933x_uart_port *up)
 {
 	struct circ_buf *xmit = &up->port.state->xmit;
-	struct serial_rs485 *rs485conf = &up->port.rs485;
+	struct kserial_rs485 *rs485conf = &up->port.rs485;
 	int count;
 	bool half_duplex_send = false;
 
@@ -581,7 +581,7 @@  static const struct uart_ops ar933x_uart_ops = {
 };
 
 static int ar933x_config_rs485(struct uart_port *port, struct ktermios *termios,
-				struct serial_rs485 *rs485conf)
+				struct kserial_rs485 *rs485conf)
 {
 	return 0;
 }
@@ -693,8 +693,8 @@  static struct uart_driver ar933x_uart_driver = {
 	.cons		= NULL, /* filled in runtime */
 };
 
-static const struct serial_rs485 ar933x_no_rs485 = {};
-static const struct serial_rs485 ar933x_rs485_supported = {
+static const struct kserial_rs485 ar933x_no_rs485 = {};
+static const struct kserial_rs485 ar933x_rs485_supported = {
 	.flags = SER_RS485_ENABLED | SER_RS485_RTS_ON_SEND | SER_RS485_RTS_AFTER_SEND,
 };
 
diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
index 30ba9eef7b39..be0296714585 100644
--- a/drivers/tty/serial/atmel_serial.c
+++ b/drivers/tty/serial/atmel_serial.c
@@ -284,7 +284,7 @@  static void atmel_tasklet_schedule(struct atmel_uart_port *atmel_port,
 
 /* Enable or disable the rs485 support */
 static int atmel_config_rs485(struct uart_port *port, struct ktermios *termios,
-			      struct serial_rs485 *rs485conf)
+			      struct kserial_rs485 *rs485conf)
 {
 	struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
 	unsigned int mode;
@@ -2471,7 +2471,7 @@  static const struct uart_ops atmel_pops = {
 #endif
 };
 
-static const struct serial_rs485 atmel_rs485_supported = {
+static const struct kserial_rs485 atmel_rs485_supported = {
 	.flags = SER_RS485_ENABLED | SER_RS485_RTS_AFTER_SEND | SER_RS485_RX_DURING_TX,
 	.delay_rts_before_send = 1,
 	.delay_rts_after_send = 1,
diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
index f6c33cd228c8..7b28cb8bee1e 100644
--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -1374,7 +1374,7 @@  static void lpuart_dma_rx_free(struct uart_port *port)
 }
 
 static int lpuart_config_rs485(struct uart_port *port, struct ktermios *termios,
-			struct serial_rs485 *rs485)
+			struct kserial_rs485 *rs485)
 {
 	struct lpuart_port *sport = container_of(port,
 			struct lpuart_port, port);
@@ -1404,7 +1404,7 @@  static int lpuart_config_rs485(struct uart_port *port, struct ktermios *termios,
 }
 
 static int lpuart32_config_rs485(struct uart_port *port, struct ktermios *termios,
-			struct serial_rs485 *rs485)
+			struct kserial_rs485 *rs485)
 {
 	struct lpuart_port *sport = container_of(port,
 			struct lpuart_port, port);
@@ -2633,7 +2633,7 @@  static struct uart_driver lpuart_reg = {
 	.cons		= LPUART_CONSOLE,
 };
 
-static const struct serial_rs485 lpuart_rs485_supported = {
+static const struct kserial_rs485 lpuart_rs485_supported = {
 	.flags = SER_RS485_ENABLED | SER_RS485_RTS_ON_SEND | SER_RS485_RTS_AFTER_SEND,
 	/* delay_rts_* and RX_DURING_TX are not supported */
 };
diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 522445a8f666..0768e8270153 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -1908,7 +1908,7 @@  static void imx_uart_poll_put_char(struct uart_port *port, unsigned char c)
 
 /* called with port.lock taken and irqs off or from .probe without locking */
 static int imx_uart_rs485_config(struct uart_port *port, struct ktermios *termios,
-				 struct serial_rs485 *rs485conf)
+				 struct kserial_rs485 *rs485conf)
 {
 	struct imx_port *sport = (struct imx_port *)port;
 	u32 ucr2;
@@ -2196,8 +2196,8 @@  static enum hrtimer_restart imx_trigger_stop_tx(struct hrtimer *t)
 	return HRTIMER_NORESTART;
 }
 
-static const struct serial_rs485 imx_no_rs485 = {};	/* No RS485 if no RTS */
-static const struct serial_rs485 imx_rs485_supported = {
+static const struct kserial_rs485 imx_no_rs485 = {};	/* No RS485 if no RTS */
+static const struct kserial_rs485 imx_rs485_supported = {
 	.flags = SER_RS485_ENABLED | SER_RS485_RTS_ON_SEND | SER_RS485_RTS_AFTER_SEND |
 		 SER_RS485_RX_DURING_TX,
 	.delay_rts_before_send = 1,
diff --git a/drivers/tty/serial/max310x.c b/drivers/tty/serial/max310x.c
index ab10ca4a45b5..6a8ab63d1072 100644
--- a/drivers/tty/serial/max310x.c
+++ b/drivers/tty/serial/max310x.c
@@ -1037,7 +1037,7 @@  static void max310x_rs_proc(struct work_struct *ws)
 }
 
 static int max310x_rs485_config(struct uart_port *port, struct ktermios *termios,
-				struct serial_rs485 *rs485)
+				struct kserial_rs485 *rs485)
 {
 	struct max310x_one *one = to_max310x_port(port);
 
@@ -1257,7 +1257,7 @@  static int max310x_gpio_set_config(struct gpio_chip *chip, unsigned int offset,
 }
 #endif
 
-static const struct serial_rs485 max310x_rs485_supported = {
+static const struct kserial_rs485 max310x_rs485_supported = {
 	.flags = SER_RS485_ENABLED | SER_RS485_RTS_ON_SEND | SER_RS485_RX_DURING_TX,
 	.delay_rts_before_send = 1,
 	.delay_rts_after_send = 1,
diff --git a/drivers/tty/serial/mcf.c b/drivers/tty/serial/mcf.c
index f4aaaadd0742..9c86218ae29d 100644
--- a/drivers/tty/serial/mcf.c
+++ b/drivers/tty/serial/mcf.c
@@ -432,7 +432,7 @@  static int mcf_verify_port(struct uart_port *port, struct serial_struct *ser)
 
 /* Enable or disable the RS485 support */
 static int mcf_config_rs485(struct uart_port *port, struct ktermios *termios,
-			    struct serial_rs485 *rs485)
+			    struct kserial_rs485 *rs485)
 {
 	unsigned char mr1, mr2;
 
@@ -453,7 +453,7 @@  static int mcf_config_rs485(struct uart_port *port, struct ktermios *termios,
 	return 0;
 }
 
-static const struct serial_rs485 mcf_rs485_supported = {
+static const struct kserial_rs485 mcf_rs485_supported = {
 	.flags = SER_RS485_ENABLED | SER_RS485_RTS_AFTER_SEND,
 };
 
diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c
index 0aa666e247d5..013d843833a9 100644
--- a/drivers/tty/serial/omap-serial.c
+++ b/drivers/tty/serial/omap-serial.c
@@ -1325,7 +1325,7 @@  static inline void serial_omap_add_console_port(struct uart_omap_port *up)
 /* Enable or disable the rs485 support */
 static int
 serial_omap_config_rs485(struct uart_port *port, struct ktermios *termios,
-			 struct serial_rs485 *rs485)
+			 struct kserial_rs485 *rs485)
 {
 	struct uart_omap_port *up = to_uart_omap_port(port);
 	unsigned int mode;
@@ -1516,7 +1516,7 @@  static struct omap_uart_port_info *of_get_uart_port_info(struct device *dev)
 static int serial_omap_probe_rs485(struct uart_omap_port *up,
 				   struct device *dev)
 {
-	struct serial_rs485 *rs485conf = &up->port.rs485;
+	struct kserial_rs485 *rs485conf = &up->port.rs485;
 	struct device_node *np = dev->of_node;
 	enum gpiod_flags gflags;
 	int ret;
@@ -1559,7 +1559,7 @@  static int serial_omap_probe_rs485(struct uart_omap_port *up,
 	return 0;
 }
 
-static const struct serial_rs485 serial_omap_rs485_supported = {
+static const struct kserial_rs485 serial_omap_rs485_supported = {
 	.flags = SER_RS485_ENABLED | SER_RS485_RTS_ON_SEND | SER_RS485_RTS_AFTER_SEND |
 		 SER_RS485_RX_DURING_TX,
 	.delay_rts_before_send = 1,
diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
index 259e08cc347c..e21f30d9fb2f 100644
--- a/drivers/tty/serial/sc16is7xx.c
+++ b/drivers/tty/serial/sc16is7xx.c
@@ -836,7 +836,7 @@  static void sc16is7xx_reconf_rs485(struct uart_port *port)
 	const u32 mask = SC16IS7XX_EFCR_AUTO_RS485_BIT |
 			 SC16IS7XX_EFCR_RTS_INVERT_BIT;
 	u32 efcr = 0;
-	struct serial_rs485 *rs485 = &port->rs485;
+	struct kserial_rs485 *rs485 = &port->rs485;
 	unsigned long irqflags;
 
 	spin_lock_irqsave(&port->lock, irqflags);
@@ -1128,7 +1128,7 @@  static void sc16is7xx_set_termios(struct uart_port *port,
 }
 
 static int sc16is7xx_config_rs485(struct uart_port *port, struct ktermios *termios,
-				  struct serial_rs485 *rs485)
+				  struct kserial_rs485 *rs485)
 {
 	struct sc16is7xx_port *s = dev_get_drvdata(port->dev);
 	struct sc16is7xx_one *one = to_sc16is7xx_one(port, port);
@@ -1353,7 +1353,7 @@  static int sc16is7xx_gpio_direction_output(struct gpio_chip *chip,
 }
 #endif
 
-static const struct serial_rs485 sc16is7xx_rs485_supported = {
+static const struct kserial_rs485 sc16is7xx_rs485_supported = {
 	.flags = SER_RS485_ENABLED | SER_RS485_RTS_AFTER_SEND,
 	.delay_rts_before_send = 1,
 	.delay_rts_after_send = 1,	/* Not supported but keep returning -EINVAL */
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 6d57cfdeda9d..4e2ffee2cabc 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -1291,7 +1291,7 @@  static int uart_get_icount(struct tty_struct *tty,
 				 SER_RS485_RTS_AFTER_SEND | SER_RS485_RX_DURING_TX | \
 				 SER_RS485_TERMINATE_BUS)
 
-static int uart_check_rs485_flags(struct uart_port *port, struct serial_rs485 *rs485)
+static int uart_check_rs485_flags(struct uart_port *port, struct kserial_rs485 *rs485)
 {
 	u32 flags = rs485->flags;
 
@@ -1320,7 +1320,7 @@  static int uart_check_rs485_flags(struct uart_port *port, struct serial_rs485 *r
 }
 
 static void uart_sanitize_serial_rs485_delays(struct uart_port *port,
-					      struct serial_rs485 *rs485)
+					      struct kserial_rs485 *rs485)
 {
 	if (!port->rs485_supported.delay_rts_before_send) {
 		if (rs485->delay_rts_before_send) {
@@ -1351,7 +1351,7 @@  static void uart_sanitize_serial_rs485_delays(struct uart_port *port,
 	}
 }
 
-static void uart_sanitize_serial_rs485(struct uart_port *port, struct serial_rs485 *rs485)
+static void uart_sanitize_serial_rs485(struct uart_port *port, struct kserial_rs485 *rs485)
 {
 	u32 supported_flags = port->rs485_supported.flags;
 
@@ -1378,7 +1378,7 @@  static void uart_sanitize_serial_rs485(struct uart_port *port, struct serial_rs4
 }
 
 static void uart_set_rs485_termination(struct uart_port *port,
-				       const struct serial_rs485 *rs485)
+				       const struct kserial_rs485 *rs485)
 {
 	if (!(rs485->flags & SER_RS485_ENABLED))
 		return;
@@ -1389,7 +1389,7 @@  static void uart_set_rs485_termination(struct uart_port *port,
 
 int uart_rs485_config(struct uart_port *port)
 {
-	struct serial_rs485 *rs485 = &port->rs485;
+	struct kserial_rs485 *rs485 = &port->rs485;
 	int ret;
 
 	uart_sanitize_serial_rs485(port, rs485);
@@ -1403,23 +1403,30 @@  int uart_rs485_config(struct uart_port *port)
 }
 EXPORT_SYMBOL_GPL(uart_rs485_config);
 
-static int user_rs485_to_kernel_serial_rs485(struct serial_rs485 *rs485,
+static int user_rs485_to_kernel_serial_rs485(struct kserial_rs485 *rs485,
 					     const struct serial_rs485 __user *rs485_user)
 {
-	if (copy_from_user(rs485, rs485_user, sizeof(*rs485)))
+	struct serial_rs485 rs485_uapi;
+
+	if (copy_from_user(&rs485_uapi, rs485_user, sizeof(*rs485)))
 		return -EFAULT;
 
+	*rs485 = *((struct kserial_rs485 *)&rs485_uapi);
+
 	return 0;
 }
 
 static int kernel_serial_rs485_to_user_rs485(struct serial_rs485 __user *rs485_user,
-					     struct serial_rs485 *rs485)
+					     const struct kserial_rs485 *rs485)
 {
+	struct serial_rs485 rs485_uapi;
+
+	*((struct kserial_rs485 *)&rs485_uapi) = *rs485;
 	/* Return clean padding area to userspace */
-	memset(rs485->padding0, 0, sizeof(rs485->padding0));
-	memset(rs485->padding1, 0, sizeof(rs485->padding1));
+	memset(rs485_uapi.padding0, 0, sizeof(rs485_uapi.padding0));
+	memset(rs485_uapi.padding1, 0, sizeof(rs485_uapi.padding1));
 
-	if (copy_to_user(rs485_user, rs485, sizeof(*rs485)))
+	if (copy_to_user(rs485_user, &rs485_uapi, sizeof(rs485_uapi)))
 		return -EFAULT;
 
 	return 0;
@@ -1429,7 +1436,7 @@  static int uart_get_rs485_config(struct uart_port *port,
 			 struct serial_rs485 __user *rs485_user)
 {
 	unsigned long flags;
-	struct serial_rs485 rs485;
+	struct kserial_rs485 rs485;
 
 	spin_lock_irqsave(&port->lock, flags);
 	rs485 = port->rs485;
@@ -1441,7 +1448,7 @@  static int uart_get_rs485_config(struct uart_port *port,
 static int uart_set_rs485_config(struct tty_struct *tty, struct uart_port *port,
 			 struct serial_rs485 __user *rs485_user)
 {
-	struct serial_rs485 rs485;
+	struct kserial_rs485 rs485;
 	int ret;
 	unsigned long flags;
 
@@ -3415,7 +3422,7 @@  EXPORT_SYMBOL_GPL(uart_try_toggle_sysrq);
  */
 int uart_get_rs485_mode(struct uart_port *port)
 {
-	struct serial_rs485 *rs485conf = &port->rs485;
+	struct kserial_rs485 *rs485conf = &port->rs485;
 	struct device *dev = port->dev;
 	u32 rs485_delay[2];
 	int ret;
@@ -3471,6 +3478,19 @@  int uart_get_rs485_mode(struct uart_port *port)
 }
 EXPORT_SYMBOL_GPL(uart_get_rs485_mode);
 
+/* Compile-time asserts for kserial_rs485 and serial_rs485 equality (except padding) */
+static_assert(offsetof(struct kserial_rs485, flags) ==
+	      offsetof(struct serial_rs485, flags));
+static_assert(offsetof(struct kserial_rs485, delay_rts_before_send) ==
+	      offsetof(struct serial_rs485, delay_rts_before_send));
+static_assert(offsetof(struct kserial_rs485, delay_rts_after_send) ==
+	      offsetof(struct serial_rs485, delay_rts_after_send));
+static_assert(offsetof(struct kserial_rs485, addr_recv) ==
+	      offsetof(struct serial_rs485, addr_recv));
+static_assert(offsetof(struct kserial_rs485, addr_dest) ==
+	      offsetof(struct serial_rs485, addr_dest));
+static_assert(sizeof(struct kserial_rs485) <= sizeof(struct serial_rs485));
+
 /* Compile-time assertions for serial_rs485 layout */
 static_assert(offsetof(struct serial_rs485, padding) ==
               (offsetof(struct serial_rs485, delay_rts_after_send) + sizeof(__u32)));
diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index 2c85dbf165c4..8606bda9f7fa 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -169,7 +169,7 @@  static void stm32_usart_config_reg_rs485(u32 *cr1, u32 *cr3, u32 delay_ADE,
 }
 
 static int stm32_usart_config_rs485(struct uart_port *port, struct ktermios *termios,
-				    struct serial_rs485 *rs485conf)
+				    struct kserial_rs485 *rs485conf)
 {
 	struct stm32_port *stm32_port = to_stm32_port(port);
 	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
@@ -220,7 +220,7 @@  static int stm32_usart_config_rs485(struct uart_port *port, struct ktermios *ter
 static int stm32_usart_init_rs485(struct uart_port *port,
 				  struct platform_device *pdev)
 {
-	struct serial_rs485 *rs485conf = &port->rs485;
+	struct kserial_rs485 *rs485conf = &port->rs485;
 
 	rs485conf->flags = 0;
 	rs485conf->delay_rts_before_send = 0;
@@ -532,7 +532,7 @@  static void stm32_usart_tc_interrupt_disable(struct uart_port *port)
 static void stm32_usart_rs485_rts_enable(struct uart_port *port)
 {
 	struct stm32_port *stm32_port = to_stm32_port(port);
-	struct serial_rs485 *rs485conf = &port->rs485;
+	struct kserial_rs485 *rs485conf = &port->rs485;
 
 	if (stm32_port->hw_flow_control ||
 	    !(rs485conf->flags & SER_RS485_ENABLED))
@@ -550,7 +550,7 @@  static void stm32_usart_rs485_rts_enable(struct uart_port *port)
 static void stm32_usart_rs485_rts_disable(struct uart_port *port)
 {
 	struct stm32_port *stm32_port = to_stm32_port(port);
-	struct serial_rs485 *rs485conf = &port->rs485;
+	struct kserial_rs485 *rs485conf = &port->rs485;
 
 	if (stm32_port->hw_flow_control ||
 	    !(rs485conf->flags & SER_RS485_ENABLED))
@@ -1094,7 +1094,7 @@  static void stm32_usart_set_termios(struct uart_port *port,
 	struct stm32_port *stm32_port = to_stm32_port(port);
 	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
 	const struct stm32_usart_config *cfg = &stm32_port->info->cfg;
-	struct serial_rs485 *rs485conf = &port->rs485;
+	struct kserial_rs485 *rs485conf = &port->rs485;
 	unsigned int baud, bits;
 	u32 usartdiv, mantissa, fraction, oversampling;
 	tcflag_t cflag = termios->c_cflag;
@@ -1446,7 +1446,7 @@  static void stm32_usart_deinit_port(struct stm32_port *stm32port)
 	clk_disable_unprepare(stm32port->clk);
 }
 
-static const struct serial_rs485 stm32_rs485_supported = {
+static const struct kserial_rs485 stm32_rs485_supported = {
 	.flags = SER_RS485_ENABLED | SER_RS485_RTS_ON_SEND | SER_RS485_RTS_AFTER_SEND |
 		 SER_RS485_RX_DURING_TX,
 	.delay_rts_before_send = 1,
diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index aef3145f2032..3fe02e74873a 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -31,6 +31,20 @@  struct serial_struct;
 struct device;
 struct gpio_desc;
 
+/*
+ * Must match with serial_rs485 in include/uapi/linux/serial.h excluding the
+ * padding.
+ */
+struct kserial_rs485 {
+	__u32	flags;			/* RS485 feature flags */
+	__u32	delay_rts_before_send;	/* Delay before send (milliseconds) */
+	__u32	delay_rts_after_send;	/* Delay after send (milliseconds) */
+	struct {
+		__u8    addr_recv;
+		__u8    addr_dest;
+	};
+};
+
 /**
  * struct uart_ops -- interface between serial_core and the driver
  *
@@ -447,7 +461,7 @@  struct uart_port {
 	void			(*handle_break)(struct uart_port *);
 	int			(*rs485_config)(struct uart_port *,
 						struct ktermios *termios,
-						struct serial_rs485 *rs485);
+						struct kserial_rs485 *rs485);
 	int			(*iso7816_config)(struct uart_port *,
 						  struct serial_iso7816 *iso7816);
 	unsigned int		irq;			/* irq number */
@@ -567,8 +581,8 @@  struct uart_port {
 	const char		*name;			/* port name */
 	struct attribute_group	*attr_group;		/* port specific attributes */
 	const struct attribute_group **tty_groups;	/* all attributes (serial core use only) */
-	struct serial_rs485     rs485;
-	struct serial_rs485	rs485_supported;	/* Supported mask for serial_rs485 */
+	struct kserial_rs485	rs485;
+	struct kserial_rs485	rs485_supported;	/* Supported mask for serial_rs485 */
 	struct gpio_desc	*rs485_term_gpio;	/* enable RS485 bus termination */
 	struct serial_iso7816   iso7816;
 	void			*private_data;		/* generic platform data pointer */
diff --git a/include/uapi/linux/serial.h b/include/uapi/linux/serial.h
index cea06924b295..95583e99a798 100644
--- a/include/uapi/linux/serial.h
+++ b/include/uapi/linux/serial.h
@@ -112,8 +112,9 @@  struct serial_icounter_struct {
  * support. Set with TIOCSRS485 and get with TIOCGRS485 if supported by your
  * platform. The set function returns the new state, with any unsupported bits
  * reverted appropriately.
+ *
+ * There's kernel counterpart kserial_rs485 of this struct without padding.
  */
-
 struct serial_rs485 {
 	__u32	flags;			/* RS485 feature flags */
 #define SER_RS485_ENABLED		(1 << 0)	/* If enabled */