linux-kernel - Re: mmc does not work in qemu n900

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Date:	Fri, 25 Dec 2015 13:57:42 +0100
From:	Pali Rohár <pali.rohar@...il.com>
To:	Chris Ball <chris@...ntf.net>
Cc:	Ulf Hansson <ulf.hansson@...aro.org>, linux-mmc@...r.kernel.org,
	linux-kernel@...r.kernel.org, Pavel Machek <pavel@....cz>,
	Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>,
	Sebastian Reichel <sre@...nel.org>,
	Aaro Koskinen <aaro.koskinen@....fi>
Subject: Re: mmc does not work in qemu n900

On Monday 26 January 2015 22:04:59 Pali Rohár wrote:
> Hello,
> 
> for unknown reason kernel in qemu n900 machine is not able to
> detect internal eMMC memory. External SD card is detected without
> problem.
> 
> If I apply this one-line patch eMMC in qemu start working:
> 
> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
> index 9584bff..0d4461c 100644
> --- a/drivers/mmc/core/core.c
> +++ b/drivers/mmc/core/core.c
> @@ -2337,6 +2337,9 @@ static int mmc_rescan_try_freq(
>  		return 0;
>  	if (!mmc_attach_sd(host))
>  		return 0;
> +
> +	mmc_go_idle(host);
> +
>  	if (!mmc_attach_mmc(host))
>  		return 0;
> 
> I played with mmc and qemu n900 a bit and also this simple patch
> (without first) fix problem (that mmc is not detected by kernel):
> 
> diff --git a/drivers/mmc/core/mmc_ops.c
> b/drivers/mmc/core/mmc_ops.c
> index 3b044c5..0c93a2c 100644
> --- a/drivers/mmc/core/mmc_ops.c
> +++ b/drivers/mmc/core/mmc_ops.c
> @@ -157,6 +157,10 @@ int mmc_send_op_cond(
> 
>  	BUG_ON(!host);
> 
> +	/* reset mmc before calling op_cond */
> +	memset(&cmd, 0, sizeof(struct mmc_command));
> +	mmc_wait_for_cmd(host, &cmd, MMC_CMD_RETRIES);
> +
>  	cmd.opcode = MMC_SEND_OP_COND;
>  	cmd.arg = mmc_host_is_spi(host) ? 0 : ocr;
>  	cmd.flags = MMC_RSP_SPI_R1 | MMC_RSP_R3 | MMC_CMD_BCR;
> 
> 
> I have no idea where is problem. I also do not understand mmc
> kernel code, but second patch I have on my HDD since 2.6.37.
> 
> Can somebody with knowledge of mmc subsystem look at this
> problem? Why any of these two patches fix problem when mmc is not
> detected by kernel in qemu (machine n900)? Detection of mmc fails
> because function mmc_send_op_cond() without one of above patches
> fails.

I will bring this tread to front again as mmc without one of provided 
patches does not work with 4.4-rc6 kernel in N900 qemu.

-- 
Pali Rohár
pali.rohar@...il.com

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