linux-kernel - Re: [PATCH v1 3/3] spi: xilinx: Make num_chipselect 8-bit in the struct xspi_platform

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Message-ID: <f7a882c8-5858-4d6b-8a70-0702c3170661@amd.com>
Date: Fri, 8 Mar 2024 09:20:23 +0100
From: Michal Simek <michal.simek@....com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
 linux-spi@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org
Cc: Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH v1 3/3] spi: xilinx: Make num_chipselect 8-bit in the
 struct xspi_platform_data



On 3/7/24 16:43, Andy Shevchenko wrote:
> There is no use for whole 16-bit for the number of chip select pins.
> Drop it to 8 bits and reshuffle the data structure layout to avoid
> unnecessary paddings.
> 
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> ---
>   include/linux/spi/xilinx_spi.h | 12 ++++++------
>   1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/spi/xilinx_spi.h b/include/linux/spi/xilinx_spi.h
> index 4ba8f53ce570..a638ba2a55bd 100644
> --- a/include/linux/spi/xilinx_spi.h
> +++ b/include/linux/spi/xilinx_spi.h
> @@ -8,18 +8,18 @@ struct spi_board_info;
>   
>   /**
>    * struct xspi_platform_data - Platform data of the Xilinx SPI driver
> + * @force_irq:		If set, forces QSPI transaction requirements.
>    * @num_chipselect:	Number of chip select by the IP.
>    * @bits_per_word:	Number of bits per word.
> - * @devices:		Devices to add when the driver is probed.
>    * @num_devices:	Number of devices in the devices array.
> - * @force_irq:		If set, forces QSPI transaction requirements.
> + * @devices:		Devices to add when the driver is probed.
>    */
>   struct xspi_platform_data {
> -	u16 num_chipselect;
> -	u8 bits_per_word;
> -	struct spi_board_info *devices;
> -	u8 num_devices;
>   	bool force_irq;
> +	u8 num_chipselect;
> +	u8 bits_per_word;
> +	u8 num_devices;

all above have 32bits. It means on 64bit cpu you have 32bit gap here.

> +	struct spi_board_info *devices;


It means this should be like this and then there is no gap between on 
32bit/64bit systems.

struct xspi_platform_data {
	struct spi_board_info *    devices;              /*     0     8 */
	bool                       force_irq;            /*     8     1 */
	u8                         num_chipselect;       /*     9     1 */
	u8                         bits_per_word;        /*    10     1 */
	u8                         num_devices;          /*    11     1 */

	/* size: 16, cachelines: 1, members: 5 */
	/* padding: 4 */
	/* last cacheline: 16 bytes */
};

Thanks,
Michal