[Letux-kernel] [PATCH 00/20] A bunch of JZ4730 fixups for letux-kernel

[Paul Boddie]

On Saturday, 12 December 2020 12:04:31 CET H. Nikolaus Schaller wrote:
> 
> Thanks for the patch!
> 
> It has changed something:
> 
> [    0.157233] Waiting for root device /dev/mmcblk1p2...
> [    0.157380] mmc0: unrecognised SCR structure version 4
> [    0.162797] mmc0: error -22 whilst initialising SD card
> [    0.172349] mmc0: card never left busy state
> [    0.176875] mmc0: error -145 whilst initialising SD card
> [    0.192446] mmc0: card never left busy state
> [    0.196970] mmc0: error -145 whilst initialising SD card
> [    0.212861] mmc0: card never left busy state
> [    0.217387] mmc0: error -145 whilst initialising SD card
> 
> The mmc0: messages are new.

I guess these messages could easily occur with bad read operations where the 
transfers just produce nonsense or nothing, but there might be something else 
involved.

> With some printk:
> 
> [    0.177922] ALSA device list:
> [    0.181085]   No soundcards found.
> [    0.170902] mmc_gpio_set_rs
> [    0.169238] mmc_gpio_set_rs
> [    0.172284] mmc_gpiod_request_cd_irq
> [    0.177171] mmc_gpio_get_cd
> [    0.180338] jz4740-mmc 10021000.mmc: Ingenic SD/MMC card driver
> registered
> [    0.170315] jz4740-mmc 10021000.mmc: Using DMA, 4-bit mode
> [    0.182508] Waiting for root device /dev/mmcblk1p2...
> [    0.182818] mmc0: unrecognised SCR structure version 4
> [    0.188236] mmc0: error -22 whilst initialising SD card
> [    0.177274] mmc_gpio_set_rs
> [    0.177907] mmc_gpio_set_rs
> [    0.197028] mmc0: card never left busy state
> [    0.201554] mmc0: error -145 whilst initialising SD card
> [    0.197475] mmc_gpio_set_rs
> [    0.197603] mmc_gpio_set_rs
> [    0.217022] mmc0: card never left busy state
> [    0.221546] mmc0: error -145 whilst initialising SD card
> [    0.217489] mmc_gpio_set_rs
> [    0.217598] mmc_gpio_set_rs
> [    0.237292] mmc0: card never left busy state
> [    0.241818] mmc0: error -145 whilst initialising SD card
> 
> I think I should print some values from mmc_gpio_set_rs,
> mmc_gpiod_request_cd_irq, mmc_gpio_get_cd.

Yes, the mmc_gpio_set_rs calls are probably related to power cycling, done by 
mmc_power_up.

> And it *may* be that it has something to do with:
> 
> https://www.spinics.net/lists/arm-kernel/msg40834.html (they removed the
> check for SCR structure version)

I don't think this is likely to be the solution. :-)

> https://www.at91.com/viewtopic.php?t=28764
> https://unix.stackexchange.com/questions/492611/mmc0-warning-on-sd-card-boot
> up-of-linux (here it did go away with kernel v4.20)
> https://e2e.ti.com/support/processors/f/791/t/263734?System-sometimes-stuck
> -at-Waiting-for-root-device-dev-mmcblk0p2-during-boot (here it was a CD
> hardware issue)

Yes, I think many of these just indicate that something else is going wrong.

> Anyways the error comes from
> 
> https://elixir.bootlin.com/linux/latest/source/drivers/mmc/core/sd.c#L184
> 
> and is *after* trying to read something from the SD. Either the SD card pins
> are not configured properly or our broken DMA makes problems.
> 
> Do you know the location where the decision to choose DMA or not-DMA mode is
> made?

In drivers/mmc/host/jz4740_mmc.c within the function jz4740_mmc_probe:

        ret = jz4740_mmc_acquire_dma_channels(host);
        if (ret == -EPROBE_DEFER)
                goto err_free_irq;
        host->use_dma = !ret;

And in the function jz4740_mmc_acquire_dma_channels:

        host->dma_tx = dma_request_chan(mmc_dev(host->mmc), "tx");
        ...
        host->dma_rx = dma_request_chan(mmc_dev(host->mmc), "rx");

If you do not get a message saying "Failed to get dma_tx channel" or similar, 
then the channels are acquired. Indeed, the "Using DMA, 4-bit mode" confirms 
this.

It's probable that the DMA transfers aren't working. I guess I could try and 
investigate this in other environments just to see if I have paid attention to 
all the relevant details. My modifications to the driver are just tentative, 
after all.

Paul