Re: [v8] media: imx: add mem2mem device

[Sven Van Asbroeck <thesven73@xxxxxxxxx>]

On Mon, Jun 10, 2019 at 5:09 AM Robin Gong <yibin.gong@xxxxxxx> wrote:
>
> I can reproduce once enable your config to build firmware in kernel, but no such issue
> if load sdma firmware from rootfs as imx_v6_v7_defconfig. Maybe firmware built in function
> broken by some patches. Could you try with the default firmware loading way which is from
> rootfs(/lib/firmware/imx/sdma/sdma-imx6q.bin)?

This is it ! If I add the firmware to the kernel directly, I see the crash.
But if I use the firmware fall-back mechanism, there is no crash.
And if I build imx-sdma as a module, and insmod it later, there is
also no crash.

I patched imx-sdma so it logs the adler32 checksum of the firmware it's
loading (I tried using the kernel crypto API, but it doesn't work this early
in the boot). I notice that the firmware is always the same, crash or no
crash:

firmware in-kernel (crash):
[    1.370424] imx-sdma 20ec000.sdma: firmware hash: 69BC0F09
firmware fallback (no crash):
[    6.466394] imx-sdma 20ec000.sdma: firmware hash: 69BC0F09

My guess: this could be a timing issue. If the sdma driver loads 'too early',
the boot crash will happen. Maybe the driver needs to check for a
missing dependency on boot, and -EPROBE_DEFER ?

Robin, should I make a bug report? If so, who do I send this to?

Code used to print the firmware hash on imx-sdma:

#define MOD_ADLER  65521

static u32 adler32(const unsigned char *data, size_t len)
{
    u32 a = 1, b = 0;
    size_t index;

    for (index = 0; index < len; ++index)
    {
        a = (a + data[index]) % MOD_ADLER;
        b = (b + a) % MOD_ADLER;
    }

    return (b << 16) | a;
}

static void log_fw_hash(struct device *dev, const struct firmware *fw)
{
        dev_info(dev, "firmware hash: %08X", adler32(fw->data, fw->size));
}

static void sdma_load_firmware(const struct firmware *fw, void *context)
{
        struct sdma_engine *sdma = context;
        const struct sdma_firmware_header *header;
        const struct sdma_script_start_addrs *addr;
        unsigned short *ram_code;

        if (!fw) {
                dev_info(sdma->dev, "external firmware not found,
using ROM firmware\n");
                /* In this case we just use the ROM firmware. */
                return;
        }
        log_fw_hash(sdma->dev, fw);