Messages in this thread | | | From | Vitor Soares <> | Subject | RE: [RFC 5/5] i3c: add i3cdev module to expose i3c dev in /dev | Date | Wed, 11 Dec 2019 15:07:36 +0000 |
| |
Hi Arnd,
From: Arnd Bergmann <arnd@arndb.de> Date: Tue, Dec 10, 2019 at 19:37:14
> 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.
I will try to do that.
> > > 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.
Thanks, now I know that is mandatory 😊.
> > 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
I confess that I wasn't familiar with io_submit() until now and went straightway for the ioctl() approach. So far, my understanding is that io_submit() will call .write or .read of i3cdev module depending on the iocb command. if so, we won't be able to do a repeated start between a multiple iocb in the same list, right?
Apart from this private read/write need, another requirement that leads me to use the ioctl() was: - When we support HDR command in i3c subsystem we can expand the ioctl() command to support it. - For now, device API doesn't expose CCC commands but some of them are used for a private contract between master and device and we likely need that support in the future as well.
Thanks, Best regards, Vitor Soares
| |