Re: [PATCH 1/4] xen/arm: debug-pl011: Use correct accessors

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 7 Jun 2023, Michal Orzel wrote:
> Although most PL011 UARTs can cope with 32-bit accesses, some of the old
> legacy ones might not. PL011 registers are 8/16-bit wide and this shall
> be perceived as the normal behavior.
> 
> Modify early printk pl011 code for arm32/arm64 to use the correct
> accessors depending on the register size (refer ARM DDI 0183G, Table 3.1).
> 
> Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>
> ---
> Next patch will override strX,ldrX with macros but I prefer to keep the
> history clean (+ possibiltity for a backport if needed).
> ---
>  xen/arch/arm/arm32/debug-pl011.inc | 12 ++++++------
>  xen/arch/arm/arm64/debug-pl011.inc |  6 +++---
>  2 files changed, 9 insertions(+), 9 deletions(-)
> 
> diff --git a/xen/arch/arm/arm32/debug-pl011.inc 
> b/xen/arch/arm/arm32/debug-pl011.inc
> index c527f1d4424d..9fe0c2503831 100644
> --- a/xen/arch/arm/arm32/debug-pl011.inc
> +++ b/xen/arch/arm/arm32/debug-pl011.inc
> @@ -26,13 +26,13 @@
>   */
>  .macro early_uart_init rb, rc, rd
>          mov   \rc, #(7372800 / CONFIG_EARLY_UART_PL011_BAUD_RATE % 16)
> -        str   \rc, [\rb, #FBRD]     /* -> UARTFBRD (Baud divisor fraction) */
> +        strb  \rc, [\rb, #FBRD]     /* -> UARTFBRD (Baud divisor fraction) */
>          mov   \rc, #(7372800 / CONFIG_EARLY_UART_PL011_BAUD_RATE / 16)
> -        str   \rc, [\rb, #IBRD]     /* -> UARTIBRD (Baud divisor integer) */
> +        strh  \rc, [\rb, #IBRD]     /* -> UARTIBRD (Baud divisor integer) */
>          mov   \rc, #WLEN_8          /* 8n1 */
> -        str   \rc, [\rb, #LCR_H]     /* -> UARTLCR_H (Line control) */
> +        strb  \rc, [\rb, #LCR_H]     /* -> UARTLCR_H (Line control) */
>          ldr   \rc, =(RXE | TXE | UARTEN)      /* RXE | TXE | UARTEN */
> -        str   \rc, [\rb, #CR]     /* -> UARTCR (Control Register) */
> +        strh  \rc, [\rb, #CR]     /* -> UARTCR (Control Register) */
>  .endm
>  
>  /*
> @@ -42,7 +42,7 @@
>   */
>  .macro early_uart_ready rb, rc
>  1:
> -        ldr   \rc, [\rb, #FR]       /* <- UARTFR (Flag register) */
> +        ldrh  \rc, [\rb, #FR]       /* <- UARTFR (Flag register) */
>          tst   \rc, #BUSY             /* Check BUSY bit */
>          bne   1b                    /* Wait for the UART to be ready */
>  .endm
> @@ -53,7 +53,7 @@
>   * rt: register which contains the character to transmit
>   */
>  .macro early_uart_transmit rb, rt
> -        str   \rt, [\rb, #DR]            /* -> UARTDR (Data Register) */
> +        strb  \rt, [\rb, #DR]            /* -> UARTDR (Data Register) */

Isn't UARTDR potentially 12-bit? I am not sure if we should use strb or
strh here...

Everything else checks out.


>  .endm
>  
>  /*
> diff --git a/xen/arch/arm/arm64/debug-pl011.inc 
> b/xen/arch/arm/arm64/debug-pl011.inc
> index 6d60e78c8ba3..df713eff4922 100644
> --- a/xen/arch/arm/arm64/debug-pl011.inc
> +++ b/xen/arch/arm/arm64/debug-pl011.inc
> @@ -25,13 +25,13 @@
>   */
>  .macro early_uart_init xb, c
>          mov   x\c, #(7372800 / CONFIG_EARLY_UART_PL011_BAUD_RATE % 16)
> -        strh  w\c, [\xb, #FBRD]      /* -> UARTFBRD (Baud divisor fraction) 
> */
> +        strb  w\c, [\xb, #FBRD]      /* -> UARTFBRD (Baud divisor fraction) 
> */
>          mov   x\c, #(7372800 / CONFIG_EARLY_UART_PL011_BAUD_RATE / 16)
>          strh  w\c, [\xb, #IBRD]      /* -> UARTIBRD (Baud divisor integer) */
>          mov   x\c, #WLEN_8           /* 8n1 */
> -        str   w\c, [\xb, #LCR_H]     /* -> UARTLCR_H (Line control) */
> +        strb  w\c, [\xb, #LCR_H]     /* -> UARTLCR_H (Line control) */
>          ldr   x\c, =(RXE | TXE | UARTEN)
> -        str   w\c, [\xb, #CR]        /* -> UARTCR (Control Register) */
> +        strh  w\c, [\xb, #CR]        /* -> UARTCR (Control Register) */
>  .endm
>  
>  /*
> -- 
> 2.25.1
>