linux-kernel - Re: [RFC PATCH] mmc: block: Add new ioctl to send combo commands

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Date:	Wed, 2 Sep 2015 11:28:48 -0700
From:	Olof Johansson <olof@...om.net>
To:	Jon Hunter <jonathanh@...dia.com>
Cc:	Ulf Hansson <ulf.hansson@...aro.org>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Grant Grundler <grundler@...gle.com>,
	Olof Johansson <olofj@...omium.org>,
	Seshagiri Holi <sholi@...dia.com>
Subject: Re: [RFC PATCH] mmc: block: Add new ioctl to send combo commands

Hi,

On Wed, Sep 2, 2015 at 7:21 AM, Jon Hunter <jonathanh@...dia.com> wrote:
> From: Seshagiri Holi <sholi@...dia.com>
>
> Certain eMMC devices allow vendor specific device information to be read
> via a sequence of vendor commands. These vendor commands must be issued
> in sequence and an atomic fashion. One way to support this would be to
> add an ioctl function for sending a sequence of commands to the device
> atomically as proposed here. These combo commands are simple array of
> the existing mmc_ioc_cmd structure.

This seems reasonable to me, being able to do a sequence of
back-to-back operations without system read/writes slipping through.



> diff --git a/include/uapi/linux/mmc/ioctl.h b/include/uapi/linux/mmc/ioctl.h
> index 1f5e68923929..5943e51f22b3 100644
> --- a/include/uapi/linux/mmc/ioctl.h
> +++ b/include/uapi/linux/mmc/ioctl.h
> @@ -45,8 +45,23 @@ struct mmc_ioc_cmd {
>  };
>  #define mmc_ioc_cmd_set_data(ic, ptr) ic.data_ptr = (__u64)(unsigned long) ptr
>
> -#define MMC_IOC_CMD _IOWR(MMC_BLOCK_MAJOR, 0, struct mmc_ioc_cmd)
> +/**
> + * struct mmc_ioc_combo_cmd - combo command information
> + * @num_of_cmds: number of commands to send
> + * @mmc_ioc_cmd_list: pointer to list of commands
> + */
> +struct mmc_ioc_combo_cmd {
> +       uint8_t num_of_cmds;
> +       struct mmc_ioc_cmd *mmc_ioc_cmd_list;
> +};

The size of this struct will depend on the pointer size of userspace.

It might be better to use a u64 for the pointer instead. Otherwise
you'd need a compat ioctl wrapper to copy a 32-bit pointer over on a
64-bit kernel.



-Olof
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