linux-kernel - Re: [PATCH] New AT91 MCI Driver that supports both MCI slots used at the same time

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Date:	Fri, 29 May 2009 11:27:55 -0400
From:	Joey Oravec <joravec@...wtech.com>
To:	Rob Emanuele <poorarm@...reis.com>
CC:	nicolas.ferre@...el.com, linux-arm-kernel@...ts.arm.linux.org.uk,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] New AT91 MCI Driver that supports both MCI slots used
 at the 	same time

Rob Emanuele wrote:
> This patch creates a new AT91 Multimedia Card Interface (MCI) driver
> that supports using both MCI slots at the same time.  I'm looking for
> others to test this patch on other boards within the same family of
> chips.
>
> This driver is a port the Atmel AVR32 MCI driver which uses similar silicon.
>   
I made all necessary adjustments to test this on my at91sam9261. 
Unfortunately it didn't want to initialize my card so I wasn't able to 
try some of the failures that I experience with the existing driver. I 
sent you a private email with the logs.

> +config MMC_AT91GEN2
> +	tristate "Atmel AT91 Multimedia Card Interface support 2nd gen"
> +	depends on ARCH_AT91
> +	help
>   
On linux-arm-kernel I've detailed a lot of problems involving 
WRITE_MULTIPLE_BLOCK using the at91 mmc/sd controller. In the end you 
might need to exclude certain processors or else have a gigantic 
warning. You can talk to me offline for details on my testing.

> +struct at91_mmc_slot_pdata {
> +        unsigned int            bus_width;
> +        int                     detect_pin;
> +        int                     wp_pin;
> +        int                     vcc_pin;
> +};
>   
Notice in 2.6.29 that at91_mci and most other structures call it 
"det_pin" rather than "detect_pin"

> +	if (host->need_reset) {
> +		at91_mci_write(host, AT91_MCI_CR, AT91_MCI_SWRST);
> +		at91_mci_write(host, AT91_MCI_CR, AT91_MCI_MCIEN);
> +		at91_mci_write(host, AT91_MCI_MR, host->mode_reg);
> +		host->need_reset = false;
> +	}
>   
In my experience some at91s need a reset after every single command, 
otherwise bad things happen. I think the need_reset logic is too 
conservative in this driver.

> +		/*
> +		 * WRPROOF and RDPROOF prevent overruns/underruns by
> +		 * stopping the clock when the FIFO is full/empty.
> +		 * This state is not expected to last for long.
> +		 */
> +		host->mode_reg = (AT91_MCI_CLKDIV & clkdiv) | AT91_MCI_WRPROOF
> +					| AT91_MCI_RDPROOF;
>   
These registers are not in all at91 chips especially the at91sam9261.

> +	if (pdata->slot[0].bus_width) {
> +		ret = at91mci_init_slot(host, &pdata->slot[0],
> +				AT91_MCI_SDCSEL & 0x0, 0);
> +		if (!ret)
> +			nr_slots++;
> +	}
> +	if (pdata->slot[1].bus_width) {
> +		ret = at91mci_init_slot(host, &pdata->slot[1],
> +				AT91_MCI_SDCSEL & 0x1, 1);
> +		if (!ret)
> +			nr_slots++;
> +	}
> +
> +	if (!nr_slots)
> +		goto err_init_slot;
>   
The original pdata had "wire4" which worked (but defaulted to 1-wire) as 
default uninitialized. With this new variable it's easy to register 
mmc_slot_pdata with bus_width set to zero. The difference bit me when 
testing and at least deserves a printk if not a change.

-joey
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