linux-kernel - Re: [PATCH/RFC] spi: Change modalias from a pointer to a character array

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Date:	Mon, 12 May 2008 15:18:05 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Grant Likely <grant.likely@...retlab.ca>
Cc:	linux-kernel@...r.kernel.org,
	spi-devel-general@...ts.sourceforge.net,
	dbrownell@...rs.sourceforge.net
Subject: Re: [PATCH/RFC] spi: Change modalias from a pointer to a character
 array

On Fri, 09 May 2008 11:32:28 -0600
Grant Likely <grant.likely@...retlab.ca> wrote:

> From: Grant Likely <grant.likely@...retlab.ca>
> 
> Currently, 'modalias' in the spi_device structure is a 'const char *'.
> The spi_new_device() function fills in the modalias value from a passed
> in spi_board_info data block.  Since it is a pointer copy, the new
> spi_device remains dependent on the spi_board_info structure after the
> new spi_device is registered (no other fields in spi_device directly
> depend on the spi_board_info structure; all of the other data is copied).
> 
> This causes a problem when dynamically propulating the list of attached
> SPI devices.  For example, in arch/powerpc, the list of SPI devices can
> be populated from data in the device tree.  With the current code, the
> device tree adapter must kmalloc() a new spi_board_info structure for
> each new SPI device it finds in the device tree, and there is no simple
> mechanism in place for keeping track of these allocations.
> 
> This patch changes modalias from a 'const char *' to a fixed char array.
> By copying the modalias string instead of referencing it, the dependency
> on the spi_board_info structure is eliminated and an outside caller does
> not need to maintain a separate spi_board_info allocation for each device.
> 
> If searched through the code to the best of my ability for any references
> to modalias which may be affected by this change and haven't found anything.
> It has been tested with the lite5200b platform in arch/powerpc.
> 
> Signed-off-by: Grant Likely <grant.likely@...retlab.ca>
> ---
> 
>  drivers/spi/spi.c       |    2 +-
>  include/linux/spi/spi.h |    2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
> index 1ad12af..bdf1b70 100644
> --- a/drivers/spi/spi.c
> +++ b/drivers/spi/spi.c
> @@ -229,7 +229,7 @@ struct spi_device *spi_new_device(struct spi_master *master,
>  	proxy->max_speed_hz = chip->max_speed_hz;
>  	proxy->mode = chip->mode;
>  	proxy->irq = chip->irq;
> -	proxy->modalias = chip->modalias;
> +	strncpy(proxy->modalias, chip->modalias, KOBJ_NAME_LEN);
>  
>  	snprintf(proxy->dev.bus_id, sizeof proxy->dev.bus_id,
>  			"%s.%u", master->dev.bus_id,
> diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
> index 387e428..38a080b 100644
> --- a/include/linux/spi/spi.h
> +++ b/include/linux/spi/spi.h
> @@ -82,7 +82,7 @@ struct spi_device {
>  	int			irq;
>  	void			*controller_state;
>  	void			*controller_data;
> -	const char		*modalias;
> +	char			modalias[KOBJ_NAME_LEN];
>  
>  	/*
>  	 * likely need more hooks for more protocol options affecting how

I'm not really able to work out if this is a needed-in-2.6.26 thing.  I
assumed "not".

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