Messages in this thread | | | From | Arnd Bergmann <> | Date | Mon, 20 Apr 2020 16:34:53 +0200 | Subject | Re: [PATCH v2,RESEND] misc: new driver sram_uapi for user level SRAM access |
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On Mon, Apr 20, 2020 at 5:06 AM Wang Wenhu <wenhu.wang@vivo.com> wrote: > > A generic User-Kernel interface that allows a misc device created > by it to support file-operations of ioctl and mmap to access SRAM > memory from user level. Different kinds of SRAM alloction and free > APIs could be registered by specific SRAM hardware level driver to > the available list and then be chosen by users to allocate and map > SRAM memory from user level. > > It is extremely helpful for the user space applications that require > high performance memory accesses, such as embedded networking devices > that would process data in user space, and PowerPC e500 is a case. > > Signed-off-by: Wang Wenhu <wenhu.wang@vivo.com> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> > Cc: Arnd Bergmann <arnd@arndb.de> > Cc: Christophe Leroy <christophe.leroy@c-s.fr> > Cc: Scott Wood <oss@buserror.net> > Cc: Michael Ellerman <mpe@ellerman.id.au> > Cc: Randy Dunlap <rdunlap@infradead.org> > Cc: linuxppc-dev@lists.ozlabs.org > --- > Changes since v1: addressed comments from Arnd > * Changed the ioctl cmd definitions using _IO micros > * Export interfaces for HW-SRAM drivers to register apis to available list > * Modified allocation alignment to PAGE_SIZE > * Use phys_addr_t as type of SRAM resource size and offset > * Support compat_ioctl > * Misc device name:sram
Looks much better already.
> Note: From this on, the SRAM_UAPI driver is independent to any hardware > drivers, so I would only commit the patch itself as v2, while the v1 of > it was wrapped together with patches for Freescale L2-Cache-SRAM device. > Then after, I'd create patches for Freescale L2-Cache-SRAM device as > another series.
What I meant to suggest was actually to tie it more closely to the code we already have in drivers/misc/sram.c, which already has some form of abstraction.
> +static int __init sram_uapi_init(void) > +{ > + int ret; > + > + INIT_LIST_HEAD(&sram_api_list); > + mutex_init(&sram_api_list_lock); > + > + ret = misc_register(&sram_uapi_miscdev); > + if (ret) > + pr_err("failed to register sram uapi misc device\n");
The mutex and listhead are already initialized, so this can be a one-line function
return misc_register(&sram_uapi_miscdev);
> --- /dev/null > +++ b/include/linux/sram_uapi.h
The ioctl definitions need to be in include/uapi/linux/
> @@ -0,0 +1,28 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > +#ifndef __SRAM_UAPI_H > +#define __SRAM_UAPI_H > + > +/* Set SRAM type to be accessed */ > +#define SRAM_UAPI_IOC_SET_SRAM_TYPE _IOW('S', 0, __u32) > + > +/* Allocate resource from SRAM */ > +#define SRAM_UAPI_IOC_ALLOC _IOWR('S', 1, struct res_info) > + > +/* Free allocated resource of SRAM */ > +#define SRAM_UAPI_IOC_FREE _IOW('S', 2, struct res_info)
struct res_info needs to also be defined here, so user applications can see the definition, and it has to use __u64, not phys_addr_t, to ensure the API does not depend on kernel configuraiton.
Arnd
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