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Re: [PATCH v2 28/35] xen/8250-uart: add missing definitions


  • To: dmukhin@xxxxxxxx
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Thu, 12 Dec 2024 16:07:36 +0100
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  • Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
  • Delivery-date: Thu, 12 Dec 2024 15:07:42 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 06.12.2024 05:41, Denis Mukhin via B4 Relay wrote:
> --- a/xen/include/xen/8250-uart.h
> +++ b/xen/include/xen/8250-uart.h
> @@ -32,16 +32,22 @@
>  #define UART_MCR          0x04    /* Modem control        */
>  #define UART_LSR          0x05    /* line status          */
>  #define UART_MSR          0x06    /* Modem status         */
> +#define UART_SCR          0x07    /* Scratch pad          */
>  #define UART_USR          0x1f    /* Status register (DW) */
>  #define UART_DLL          0x00    /* divisor latch (ls) (DLAB=1) */
>  #define UART_DLM          0x01    /* divisor latch (ms) (DLAB=1) */
>  #define UART_XR_EFR       0x09    /* Enhanced function register (Exar) */
>  
> +/* ns8250 emulator: range of emulated registers [0..UART_MAX-1] */
> +#define UART_MAX          (UART_SCR + 1)

There are two issues here: "max" means "highest within range", yet
you define it as "first invalid", i.e. something we'd normally call
"_NR" or "_NUM". And then, as the comment says, this is a limit the
emulation is going to expose, not something generally applicable to
UARTs of this kind. Hence the UART_ prefix alone isn't quite correct
either.

> @@ -51,12 +57,21 @@
>  #define UART_IIR_THR      0x02    /*  - tx reg. empty     */
>  #define UART_IIR_MSI      0x00    /*  - MODEM status      */
>  #define UART_IIR_BSY      0x07    /*  - busy detect (DW) */
> +#define UART_IIR_FE0      BIT(6, U) /* FIFO enable #0 */
> +#define UART_IIR_FE1      BIT(7, U) /* FIFO enable #1 */
> +#define UART_IIR_FE_MASK  (UART_IIR_FE0 | UART_IIR_FE1)

Much like BSY is a 3-bit field, aiui this is a 2-bit one.

>  /* FIFO Control Register */
> -#define UART_FCR_ENABLE   0x01    /* enable FIFO          */
> -#define UART_FCR_CLRX     0x02    /* clear Rx FIFO        */
> -#define UART_FCR_CLTX     0x04    /* clear Tx FIFO        */
> -#define UART_FCR_DMA      0x10    /* enter DMA mode       */
> +#define UART_FCR_ENABLE     BIT(0, U)   /* enable FIFO          */
> +#define UART_FCR_CLRX       BIT(1, U)   /* clear Rx FIFO        */
> +#define UART_FCR_CLTX       BIT(2, U)   /* clear Tx FIFO        */
> +#define UART_FCR_DMA        BIT(3, U)   /* enter DMA mode       */
> +#define UART_FCR_RESERVED0  BIT(4, U)   /* reserved; always 0   */
> +#define UART_FCR_RESERVED1  BIT(5, U)   /* reserved; always 0   */
> +#define UART_FCR_RTB0       BIT(6, U)   /* receiver trigger bit #0 */
> +#define UART_FCR_RTB1       BIT(7, U)   /* receiver trigger bit #1 */
> +#define UART_FCR_TRG_MASK   (UART_FCR_RTB0 | UART_FCR_RTB1)

Much like the top two bits here are, and - as Roger has said - the
reserved bits probably also should be.

> @@ -64,17 +79,17 @@
>  
>  /*
>   * Note: The FIFO trigger levels are chip specific:
> - *   RX:76 = 00  01  10  11  TX:54 = 00  01  10  11
> - * PC16550D:  1   4   8  14          xx  xx  xx  xx
> - * TI16C550A:         1   4   8  14          xx  xx  xx  xx
> - * TI16C550C:         1   4   8  14          xx  xx  xx  xx
> - * ST16C550:  1   4   8  14          xx  xx  xx  xx
> - * ST16C650:  8  16  24  28          16   8  24  30  PORT_16650V2
> - * NS16C552:  1   4   8  14          xx  xx  xx  xx
> - * ST16C654:  8  16  56  60           8  16  32  56  PORT_16654
> - * TI16C750:  1  16  32  56          xx  xx  xx  xx  PORT_16750
> - * TI16C752:  8  16  56  60           8  16  32  56
> - * Tegra:     1   4   8  14          16   8   4   1  PORT_TEGRA
> + *  RX:76 = 00  01  10  11  TX:54 = 00  01  10  11
> + * PC16550D:     1   4   8  14      xx  xx  xx  xx
> + * TI16C550A:    1   4   8  14      xx  xx  xx  xx
> + * TI16C550C:    1   4   8  14      xx  xx  xx  xx
> + * ST16C550:     1   4   8  14      xx  xx  xx  xx
> + * ST16C650:     8  16  24  28      16   8  24  30  PORT_16650V2
> + * NS16C552:     1   4   8  14      xx  xx  xx  xx
> + * ST16C654:     8  16  56  60       8  16  32  56  PORT_16654
> + * TI16C750:     1  16  32  56      xx  xx  xx  xx  PORT_16750
> + * TI16C752:     8  16  56  60       8  16  32  56
> + * Tegra:        1   4   8  14      16   8   4   1  PORT_TEGRA
>   */

While perhaps okay, the adjustment of this table still looks unrelated.
It wants at least mentioning in the description, to clarify it's an
intentional change (as opposed to e.g. being an effect of how your
editor is configured).

> @@ -96,11 +111,31 @@
>  #define UART_LCR_CONF_MODE_B 0xBF            /* Configuration mode B */
>  
>  /* Modem Control Register */
> -#define UART_MCR_DTR      0x01    /* Data Terminal Ready  */
> -#define UART_MCR_RTS      0x02    /* Request to Send      */
> -#define UART_MCR_OUT2     0x08    /* OUT2: interrupt mask */
> -#define UART_MCR_LOOP     0x10    /* Enable loopback test mode */
> -#define UART_MCR_TCRTLR   0x40    /* Access TCR/TLR (TI16C752, EFR[4]=1) */
> +#define UART_MCR_DTR            BIT(0, U)   /* Data Terminal Ready  */
> +#define UART_MCR_RTS            BIT(1, U)   /* Request to Send      */
> +#define UART_MCR_OUT1           BIT(2, U)   /* OUT1: interrupt mask */
> +#define UART_MCR_OUT2           BIT(3, U)   /* OUT2: interrupt mask */
> +#define UART_MCR_LOOP           BIT(4, U)   /* Enable loopback test mode */
> +#define UART_MCR_RESERVED0      BIT(5, U)   /* Reserved #0 */
> +#define UART_MCR_RESERVED1      BIT(6, U)   /* Reserved #1 */
> +#define UART_MCR_TCRTLR         BIT(6, U)   /* Access TCR/TLR (TI16C752, 
> EFR[4]=1) */
> +#define UART_MCR_RESERVED2      BIT(7, U)   /* Reserved #2 */
> +#define UART_MCR_MASK \
> +    (UART_MCR_DTR | UART_MCR_RTS | \
> +     UART_MCR_OUT1 | UART_MCR_OUT2 | \
> +     UART_MCR_LOOP)
> +
> +/* Modem Status Register */
> +#define UART_MSR_DCTS           BIT(0, U)   /* Change in CTS */
> +#define UART_MSR_DDSR           BIT(1, U)   /* Change in DSR */
> +#define UART_MSR_TERI           BIT(2, U)   /* Change in RI */
> +#define UART_MSR_DDCD           BIT(3, U)   /* Change in CTS */
> +#define UART_MSR_CTS            BIT(4, U)
> +#define UART_MSR_DSR            BIT(5, U)
> +#define UART_MSR_RI             BIT(6, U)
> +#define UART_MSR_DCD            BIT(7, U)

As you introduce these constants, I think you also want to switch the sole
MSR read we have to actually use them.

Jan



 


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