XMMBoot¶

• Table of contents
• XMMBoot
  • Introduction
  • High level boot process
  • Abstraction
  • GPIOs
    • Devices GPIOs assignement and drivers
    • GPIOs usage
    • Libsamsung-ipc
    • libsamsung-ipc kernel functions gpios
    • Glossary
    • SIM card presence detection
    • TODO
  • Potential privacy and security issues
    • gpio_pda_active
    • gpio_phone_active
  • Links

Introduction¶

For both libsamsung-ipc and the Linux driver it's interesting to understand better the boot of the modem in order to come with good names for the abstraction.

High level boot process¶

• On most / all the devices we need to start by powering off the modem, and the link between the SOC and the modem. This makes sure that we can reliabily boot the modem at all times.
• Then we need to configure the hardware to put the modem in loading mode and have everything ready for loading its firmware. On some device, the link needed to load the modem needs to be configured as well.
• Then we send the modem firmware to the modem
• Then on some devices we need extra step (like triggering an HSIC re-enumeration) once it's done.

Abstraction¶

• hci_power -> link_power

• Find the difference between power_on and boot_power_on
  • Look at the GPIOs and understand what they do
  • Just read the code that use the GPIOs
  • Diff both procedures
• Look which device has which XMM626X
• Add XMM6210 devices too

GPIOs¶

Devices GPIOs assignement and drivers¶

GPIOs usage¶

• Start with I9300. Assume I9300 if device is not mentioned. Mention device when not I9300
• Add more devices and mention them

Note that we don't limit ourselves to the drivers that are in use on the devices supported by Replicant.
As Samsung wrote drivers for the modem interfaces, and that the interface is similar across many different modems, other unused drivers and their comments also gives many hints about what the GPIOs are supposed to be used for.

Libsamsung-ipc¶

¹ https://git.replicant.us/replicant/kernel_samsung_smdk4412/tree/arch/arm/mach-exynos/board-m0-modems.c#n221

² https://git.replicant.us/replicant/kernel_samsung_smdk4412/tree/arch/arm/mach-exynos/board-m0-modems.c#n218

³ https://git.replicant.us/replicant/kernel_samsung_smdk4412/tree/arch/arm/mach-exynos/board-m0-modems.c#n136

⁴ https://git.replicant.us/replicant/kernel_samsung_smdk4412/tree/arch/arm/mach-exynos/board-u1-modems.c#n153

⁵ https://git.replicant.us/replicant/kernel_samsung_smdk4412/tree/arch/arm/mach-exynos/board-u1-modems.c#n151

⁶ https://git.replicant.us/replicant/kernel_samsung_smdk4412/tree/arch/arm/mach-exynos/board-u1-modems.c#n139

libsamsung-ipc <-> kernel functions <-> gpios¶

int (*modem_on)(struct modem_ctl*);

int (*modem_off)(struct modem_ctl*);

int (*modem_boot_on)(struct modem_ctl*);

int (*modem_boot_off)(struct modem_ctl*);

int (*link_ldo_enable)(bool);

Glossary¶

• BP: Baseband processor
• CP: Cellular? processor

• AP: Application processor

TODO: move in its own page and point to it

LPA: Low power mode active (Related to ULPI specs only?)

ULPI: Probably a USB PHY spec

SIM card presence detection¶

Do we really want to check the SIM card presence?

Would it be possible not to for privacy reasons?

• Boot a modem with a SIM
• Take away the SIM card
• Go to a protest with only the SIM card and a phone with no data on it to be able to call if necessary.

TODO¶

• check gpio_flm_uart_sel in smdk4412 kernel too

Potential privacy and security issues¶

gpio_pda_active¶

From cpuidle-exynos4.c we have things like that:

    cpu_pm_enter();

#if defined(CONFIG_INTERNAL_MODEM_IF) || defined(CONFIG_SAMSUNG_PHONE_TTY)
    gpio_set_value(GPIO_PDA_ACTIVE, 0);
#endif

    if (log_en)
        pr_debug("+++lpa\n")

and:

    if (log_en)
        pr_debug("---lpa\n");
#if defined(CONFIG_INTERNAL_MODEM_IF) || defined(CONFIG_SAMSUNG_PHONE_TTY)
    gpio_set_value(GPIO_PDA_ACTIVE, 1);
#endif

    cpu_pm_exit();

Does it means that we are telling the modem about each time we go in suspend to RAM?

Devices affected or not affected:

gpio_phone_active¶

From ehci-s5p.c we have things like that:

#if defined(CONFIG_UMTS_MODEM_XMM6262)
    if (pdata->get_cp_active_state && !pdata->get_cp_active_state()) {
        s5p_ehci_port_control(pdev, CP_PORT, 0);
        pr_err("mif: force port%d off by cp reset\n", CP_PORT);
    }
#endif

Does it allows the modem to trigger a re-enumeration of the HSIC bus?

Devices affected or not affected:

Links¶

• modem_modemctl_device_xmm6262.c
• https://forum.xda-developers.com/galaxy-s2/help/how-to-talk-to-modem-commands-t1471241/page4
• http://www.arteris.com/blog/bid/59433/Interchip-Connectivity-HSIC-UniPro-HSI-C2C-LLI-oh-my
  • TODO: move this link somewhere where it's more useful