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    SubjectRe: [PATCH] drivers: brcmaxi: provide amba axi functionality in separate module
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    On Thu, 21 Apr 2011 16:12:49 +0200, Arnd Bergmann <arnd@arndb.de> wrote:

    > On Wednesday 20 April 2011, Arend van Spriel wrote:
    >> The open-source community is looking for a library which will detect
    >> cores in a chip using axi backplane. Another proposal has been
    >> sent by Rafał Miłecki, which registers detected cores in the linux
    >> device tree to be claimed by device drivers. This implies cores will
    >> always provide a system function to the kernel which is indepent from
    >> other cores and have very loose or no coupling. If this is not true,
    >> exceptions need to be added in the device registration process. This
    >> means knowledge of specific devices from specific vendors is sitting
    >> in a bus driver. Whether the exceptions are rarely or likely is a
    >> pending question.
    >
    > Hi Arend,
    >
    > I have two very general comments about this:
    >
    >> To feed the discussion this implementation takes a different approach.
    >> A calling entity (being a pci device driver, or SoC initialization
    >> sequence) registers a table with core identities and a callback
    >> function.
    >> It then starts the scan and for each detected core with a callback
    >> function it does the call providing the core information. Apart from
    >> that it provides some basic operations on the core.
    >>
    >> It has been tested using the brcmsmac driver (in
    >> drivers/staging/brcm80211).
    >
    > The API split between PCI and non-PCI devices appears to be
    > unhelpful. Can't you abstract the interface so that a user
    > would apply the exact same interfaces in both cases, and handle
    > the differences internally?

    Ok. that can be arranged ;-)

    >> +/* Core Codes */
    >> +#define NODEV_CORE_ID 0x700 /* Invalid coreid */
    >> +#define CC_CORE_ID 0x800 /* chipcommon core */
    >> +#define ILINE20_CORE_ID 0x801 /* iline20 core */
    >> +#define SRAM_CORE_ID 0x802 /* sram core */
    >> +#define SDRAM_CORE_ID 0x803 /* sdram core */
    >> +#define PCI_CORE_ID 0x804 /* pci core */
    >> +#define MIPS_CORE_ID 0x805 /* mips core */
    >> +#define ENET_CORE_ID 0x806 /* enet mac core */
    >> +#define CODEC_CORE_ID 0x807 /* v90 codec core */
    >> +#define USB_CORE_ID 0x808 /* usb 1.1 host/device core */
    >> +#define ADSL_CORE_ID 0x809 /* ADSL core */
    >> +#define ILINE100_CORE_ID 0x80a /* iline100 core */
    >> +#define IPSEC_CORE_ID 0x80b /* ipsec core */
    >> +#define UTOPIA_CORE_ID 0x80c /* utopia core */
    >> +#define PCMCIA_CORE_ID 0x80d /* pcmcia core */
    >> +#define SOCRAM_CORE_ID 0x80e /* internal memory core */
    >> +#define MEMC_CORE_ID 0x80f /* memc sdram core */
    >> +#define OFDM_CORE_ID 0x810 /* OFDM phy core */
    >> ...
    >
    > This list to me is a strong hint that the cores behind the AXI bridge
    > should normally be actual devices in Linux, i.e. the approach that
    > Rafał suggested. The vast majority of these is something that in Linux
    > would be operated by a device driver. The exceptions that I can see
    > are CPU cores and bus bridges, both of which we typically also represent
    > as devices in the flattened device tree, even though they typically
    > don't have a Linux driver attached to them.

    Fine. Your providing the kind of feedback I was looking for. The
    OFDM_CORE_ID is also an exception.

    So could a device driver claim multiple cores/devices to assure other
    drivers are not accessing those? I would prefer that over having
    exceptions coded in the axi bus driver, like the chipcommon core
    (CC_CORE_ID). I assume it can be done by the device table. Is that correct?

    Rafał,

    Would it be possible to make chipcommon driver optional (not doing the
    initialization)?

    Gr. AvS
    --
    "The world is indeed comic, but the joke is on mankind." — H.P. Lovecraft

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