Messages in this thread | | | From | Arnd Bergmann <> | Date | Tue, 10 Dec 2019 20:37:14 +0100 | Subject | Re: [RFC 5/5] i3c: add i3cdev module to expose i3c dev in /dev |
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On Tue, Dec 10, 2019 at 8:15 PM Vitor Soares <Vitor.Soares@synopsys.com> wrote: > From: Arnd Bergmann <arnd@arndb.de> > Date: Tue, Dec 10, 2019 at 17:51:14 > > > On Tue, Dec 10, 2019 at 4:37 PM Vitor Soares <Vitor.Soares@synopsys.com> wrote: > > > > > > +/* IOCTL commands */ > > > +#define I3C_DEV_IOC_MAGIC 0x07 > > > + > > > +struct i3c_ioc_priv_xfer { > > > + struct i3c_priv_xfer __user *xfers; /* pointers to i3c_priv_xfer */ > > > + __u32 nxfers; /* number of i3c_priv_xfer */ > > > +}; > > > + > > > +#define I3C_IOC_PRIV_XFER \ > > > + _IOW(I3C_DEV_IOC_MAGIC, 30, struct i3c_ioc_priv_xfer) > > > + > > > +#define I3C_IOC_PRIV_XFER_MAX_MSGS 42 > > > > This is not a great data structure for UAPI, please see > > https://urldefense.proofpoint.com/v2/url?u=https-3A__git.kernel.org_pub_scm_linux_kernel_git_arnd_playground.git_tree_Documentation_core-2Dapi_ioctl.rst-3Fh-3Dcompat-2Dioctl-2Dendgame-26id-3D927324b7900ee9b877691a8b237e272fabb21bf5&d=DwIBaQ&c=DPL6_X_6JkXFx7AXWqB0tg&r=qVuU64u9x77Y0Kd0PhDK_lpxFgg6PK9PateHwjb_DY0&m=5Q9WjK0o93NR7DQ9NM6So6mfdgpNnZnSaP8qMpgaC7E&s=LzzjrUQAG8fx5jkVyK73dBDrahNAvk09Cxxlx3KOiXI&e= > > > > for some background. I'm planning to submit that documentation for > > mainline integration soon. > > > > Arnd > > Thanks for sharing the document. > > My understanding is that I should use a data structure like the struct > spi_ioc_transfer, with this I may also use the same ioctl command > definition. Am I right?
Yes, that would be an example of a structure that follows the best practices from my document. It is still rather complex, so if you can make it any simpler, that would be ideal.
> In the documentation you also refer the compact_ioctl() and It is not > clear to me if the compact_ioctl() is mandatory in this case. Should I > implement it as well?
If the structure is defined like that, you just need to set ".compat_ioctl=compat_ptr_ioctl," in the file_operations structure and it will work, but you cannot skip that step.
As your interface is basically just read/write based, I wonder if there is a way to completely avoid the ioctl and instead use io_submit() as the primary interface.
Arnd
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