static int sbsa_uart_probe(struct platform_device *pdev) { struct uart_amba_port *uap; struct resource r; int portnr, ret; int baudrate; / * Check the mandatory baud rate parameter in the DT node early * so that we can easily exit with the error. */ if (pdev->dev.of_node) { struct device_node *np = pdev->dev.of_node; ret = of_property_read_u32(np, "current-speed", &baudrate); if (ret) return ret; } else { baudrate = 115200; } portnr = pl011_find_free_port(); if (portnr < 0) return portnr; uap = devm_kzalloc(&pdev->dev, sizeof(struct uart_amba_port), GFP_KERNEL); if (!uap) return -ENOMEM; ret = platform_get_irq(pdev, 0); if (ret < 0) { if (ret != -EPROBE_DEFER) dev_err(&pdev->dev, "cannot obtain irq\n"); return ret; } uap->port.irq = ret; #ifdef CONFIG_ACPI_SPCR_TABLE if (qdf2400_e44_present) { dev_info(&pdev->dev, "working around QDF2400 SoC erratum 44\n"); uap->vendor = &vendor_qdt_qdf2400_e44; } else #endif uap->vendor = &vendor_sbsa; uap->reg_offset = uap->vendor->reg_offset; uap->fifosize = 32; uap->port.iotype = uap->vendor->access_32b ? UPIO_MEM32 : UPIO_MEM; uap->port.ops = &sbsa_uart_pops; uap->fixed_baud = baudrate; snprintf(uap->type, sizeof(uap->type), "SBSA"); r = platform_get_resource(pdev, IORESOURCE_MEM, 0); ret = pl011_setup_port(&pdev->dev, uap, r, portnr); if (ret) return ret; platform_set_drvdata(pdev, uap); return pl011_register_port(uap); }在上述代码中，我需要添加一个功能：在以uefi方式启动系统时，uart驱动会读取acpi表内有关波特率的设置值，并以这个值进行串口波特率设置，请根据我的要求，在原代码中添加这一功能

可以按照以下步骤添加这个功能：

1. 在函数开头添加变量 `int baudrate_from_acpi`，表示从ACPI表中读取的波特率值。

2. 在if语句中添加对于UEFI启动的处理。可以通过检查 `efi_enabled` 变量是否为真来确定是否以UEFI方式启动系统。如果是，则需要读取ACPI表中的波特率值，可以使用 `acpi_table_parse()` 函数来读取ACPI表，具体使用方法可以参考内核中的 `drivers/acpi/tables.c` 文件中的相关代码。

3. 如果读取ACPI表成功，则将 `baudrate` 变量的值设置为从ACPI表中读取的值。否则，仍然使用默认值115200。

4. 在最后调用 `pl011_register_port()` 函数之前，将 `uap->fixed_baud` 变量的值设置为读取到的波特率值。

下面是修改后的代码：

static int sbsa_uart_probe(struct platform_device *pdev) {
    struct uart_amba_port *uap;
    struct resource r;
    int portnr, ret;
    int baudrate;
    int baudrate_from_acpi = 0;

    /* Check the mandatory baud rate parameter in the DT node early
     * so that we can easily exit with the error.
     */
    if (pdev->dev.of_node) {
        struct device_node *np = pdev->dev.of_node;
        ret = of_property_read_u32(np, "current-speed", &baudrate);
        if (ret)
            return ret;
    } else {
        baudrate = 115200;
    }

    /* Read baudrate from ACPI table if booting with UEFI */
    if (efi_enabled(EFI_BOOT) && acpi_table_parse(ACPI_SIG_SPCR, acpi_parse_spcr)) {
        baudrate_from_acpi = spcr_baudrate;
    }

    /* Use baudrate from ACPI table if available, otherwise use default value */
    baudrate = baudrate_from_acpi > 0 ? baudrate_from_acpi : baudrate;

    portnr = pl011_find_free_port();
    if (portnr < 0)
        return portnr;

    uap = devm_kzalloc(&pdev->dev, sizeof(struct uart_amba_port), GFP_KERNEL);
    if (!uap)
        return -ENOMEM;

    ret = platform_get_irq(pdev, 0);
    if (ret < 0) {
        if (ret != -EPROBE_DEFER)
            dev_err(&pdev->dev, "cannot obtain irq\n");
        return ret;
    }

#ifdef CONFIG_ACPI_SPCR_TABLE
    if (qdf2400_e44_present) {
        dev_info(&pdev->dev, "working around QDF2400 SoC erratum 44\n");
        uap->vendor = &vendor_qdt_qdf2400_e44;
    } else
#endif
        uap->vendor = &vendor_sbsa;

    uap->reg_offset = uap->vendor->reg_offset;
    uap->fifosize = 32;
    uap->port.iotype = uap->vendor->access_32b ? UPIO_MEM32 : UPIO_MEM;
    uap->port.ops = &sbsa_uart_pops;
    uap->fixed_baud = baudrate;
    snprintf(uap->type, sizeof(uap->type), "SBSA");

    r = platform_get_resource(pdev, IORESOURCE_MEM, 0);
    ret = pl011_setup_port(&pdev->dev, uap, r, portnr);
    if (ret)
        return ret;

    platform_set_drvdata(pdev, uap);

    /* Set fixed_baud value before registering the port */
    uap->fixed_baud = baudrate;

    return pl011_register_port(uap);
}