Re: [PATCH 1/4] drivers/bus: Added Freescale Management Complex APIs

From: Kim Phillips
Date: Thu Sep 18 2014 - 16:42:15 EST

On Thu, 18 Sep 2014 15:14:03 +0200
Alexander Graf <agraf@xxxxxxx> wrote:

> > Am 18.09.2014 um 06:17 schrieb German Rivera <German.Rivera@xxxxxxxxxxxxx>:
> >
> >> On 09/15/2014 06:44 PM, Kim Phillips wrote:
> >> On Thu, 11 Sep 2014 12:34:21 -0500
> >> "J. German Rivera" <German.Rivera@xxxxxxxxxxxxx> wrote:
> >>
> >>> From: "J. German Rivera" <German.Rivera@xxxxxxxxxxxxx>
> >>>
> >>> APIs to access the Management Complex (MC) hardware
> >>> module of Freescale LS2 SoCs. This patch includes
> >>> APIs to check the MC firmware version and to manipulate
> >>> DPRC objects in the MC.
> >>>
> >>> Signed-off-by: J. German Rivera <German.Rivera@xxxxxxxxxxxxx>
> >>> Signed-off-by: Stuart Yoder <stuart.yoder@xxxxxxxxxxxxx>
> >>> ---
> >>> drivers/bus/fsl-mc/dpmng.c | 93 +++++
> >>> drivers/bus/fsl-mc/dprc.c | 504 +++++++++++++++++++++++
> >>> drivers/bus/fsl-mc/fsl_dpmng_cmd.h | 83 ++++
> >>> drivers/bus/fsl-mc/fsl_dprc_cmd.h | 545 +++++++++++++++++++++++++
> >>> drivers/bus/fsl-mc/fsl_mc_sys.c | 237 +++++++++++
> >>> include/linux/fsl_dpmng.h | 120 ++++++
> >>> include/linux/fsl_dprc.h | 790 ++++++++++++++++++++++++++++++++++++
> >>> include/linux/fsl_mc_cmd.h | 182 +++++++++
> >>> include/linux/fsl_mc_sys.h | 81 ++++
> >>> 9 files changed, 2635 insertions(+)
> >>> create mode 100644 drivers/bus/fsl-mc/dpmng.c
> >>> create mode 100644 drivers/bus/fsl-mc/dprc.c
> >>> create mode 100644 drivers/bus/fsl-mc/fsl_dpmng_cmd.h
> >>> create mode 100644 drivers/bus/fsl-mc/fsl_dprc_cmd.h
> >>> create mode 100644 drivers/bus/fsl-mc/fsl_mc_sys.c
> >>> create mode 100644 include/linux/fsl_dpmng.h
> >>> create mode 100644 include/linux/fsl_dprc.h
> >>> create mode 100644 include/linux/fsl_mc_cmd.h
> >>> create mode 100644 include/linux/fsl_mc_sys.h
> >>
> >> the fsl prefix in the filename fsl_dpmng_cmd.h is redundant with
> >> its directory name fsl-mc/. Note that I find dashes ('-') in
> >> filenames make them easier to type: is there a reason we're using
> >> underscores here?
> > This is a convention that we decided early on '-' for directory names
> > and '_' for file names.

based on what?

> > unnecessarily complicated error path, plus a simpler
> >> implementation can be made if fn can return the mapped address, like
> >> so:
> >>
> >> static void __iomem *map_mc_portal(phys_addr_t mc_portal_phys_addr,
> >> uint32_t mc_portal_size)
> >> {
> >> struct resource *res;
> >> void __iomem *mapped_addr;
> >>
> >> res = request_mem_region(mc_portal_phys_addr, mc_portal_size,
> >> "mc_portal");
> >> if (!res)
> >> return NULL;
> >>
> >> mapped_addr = ioremap_nocache(mc_portal_phys_addr,
> >> mc_portal_size);
> >> if (!mapped_addr)
> >> release_mem_region(mc_portal_phys_addr, mc_portal_size);
> >>
> >> return mapped_addr;
> >> }
> >>
> >> the callsite can return -ENOMEM to its caller if returned NULL. This
> >> can be improved even further if devm_ functions are used: this is
> >> just an example of how to simplify the code using early returns
> >> instead of goto error.
> >
> > I disagree. Having a common error return point is more maintainable than having multiple returns as having the clean-up logic in one place is more maintainable and makes the min path (non-error) more readable.

my comment is not that much different from Joe's here:

https://lkml.org/lkml/2014/9/17/381

but hopefully all this will change with a devm_ based implementation.

> >>> +int __must_check fsl_create_mc_io(phys_addr_t mc_portal_phys_addr,
> >>> + uint32_t mc_portal_size,
> >>> + uint32_t flags, struct fsl_mc_io **new_mc_io)
> >>> +{
> >>> + int error = -EINVAL;
> >>> + struct fsl_mc_io *mc_io = NULL;
> >>> +
> >>> + mc_io = kzalloc(sizeof(*mc_io), GFP_KERNEL);
> >>> + if (mc_io == NULL) {
> >>> + error = -ENOMEM;
> >>> + pr_err("No memory to allocate mc_io\n");
> >>> + goto error;
> >>> + }
> >>> +
> >>> + mc_io->magic = FSL_MC_IO_MAGIC;
> >>> + mc_io->flags = flags;
> >>> + mc_io->portal_phys_addr = mc_portal_phys_addr;
> >>> + mc_io->portal_size = mc_portal_size;
> >>> + spin_lock_init(&mc_io->spinlock);
> >>> + error = map_mc_portal(mc_portal_phys_addr,
> >>> + mc_portal_size, &mc_io->portal_virt_addr);
> >>> + if (error < 0)
> >>> + goto error;
> >>> +
> >>> + *new_mc_io = mc_io;
> >>> + return 0;
> >>
> >> if a fn only returns an address or error, it can return ERR_PTR
> >> (e.g., -ENOMEM), and the callsite use IS_ERR() to determine whether
> >> there was an error or address returned. This makes code much
> >> simpler instead of passing address values back by reference.
> > I disagree. I don't see why the alternative you suggest makes the code "much simpler".

because it eliminates the need for the extra pass-by-reference
argument struct fsl_mc_io **new_mc_io.

> >>> +void fsl_destroy_mc_io(struct fsl_mc_io *mc_io)
> >>> +{
> >>> + if (WARN_ON(mc_io->magic != FSL_MC_IO_MAGIC))
> >>> + return;
> >>> +
> >>> + if (mc_io->portal_virt_addr != NULL) {
> >>> + unmap_mc_portal(mc_io->portal_phys_addr,
> >>> + mc_io->portal_size, mc_io->portal_virt_addr);
> >>
> >> unmap_mc_portal already checks for virt_addr, this is another
> >> example where the code goes too far checking for NULL.
> > I disagree. Having the extra check is harmless and more importantly makes the intent explicit that we should only call unmap_mc_portal if we called map_mc_portal earlier.

the code is doing this:

if (mc_io->portal_virt_addr != NULL) {
if (WARN_ON(mc_portal_virt_addr == NULL))
return;

which is redundant and therefore makes it unnecessarily complicated,
after all, a stack trace will occur if mc_portal_virt_addr is
referenced anyway, making the WARN_ON clause redundant, too.

> >>> + mc_io->portal_virt_addr = NULL;
> >>> + }
> >>> +
> >>> + mc_io->magic = 0x0;
> >>> + kfree(mc_io);
> >>> +}

btw, what's the point of zeroing out things that are being freed?

> >>> +/**
> >>> + * @brief Management Complex firmware version information
> >>> + */
> >>> +#define MC_VER_MAJOR 2
> >>> +#define MC_VER_MINOR 0
> >>
> >> code should be adjusted to run on all *compatible* versions of h/w,
> >> not strictly the one set in these defines.
> > This comment is not precise enough be actionable.
> > What exactly you want to be changed here?
>
> I think the easy thing to do is to convert the exact version check into a ranged version check: have minimum and maximum versions you support. Or a list of exact versions you support. Or not check for the version at all - or only for the major version and guarantee that the major version indicates backwards compatibility.

yes, this was my point: elsewhere I noticed the code denies to run
iff those defines are not matched exactly: that code should change
to run as Alex describes.

> >>> +/**
> >>> + * @brief Disconnects one endpoint to remove its network link
> >>> + *
> >>> + * @param[in] mc_io Pointer to opaque I/O object
> >>> + * @param[in] dprc_handle Handle to the DPRC object
> >>> + * @param[in] endpoint Endpoint configuration parameters.
> >>> + *
> >>> + * @returns '0' on Success; Error code otherwise.
> >>> + * */
> >>> +int dprc_disconnect(struct fsl_mc_io *mc_io, uint16_t dprc_handle,
> >>> + struct dprc_endpoint *endpoint);
> >>> +
> >>> +/*! @} */
> >>
> >> this entire file is riddled with non-kernel-doc comment markers: see
> >> Documentation/kernel-doc-nano-HOWTO.txt on how to write function and
> >> other types of comments in a kernel-doc compliant format.
> > This is because this file is using doxygen comments, as it was developed
> > by another team. Unless someone else has an objection, I will leave the doxygen comments alone and not make any change here.
>
> Do you see any other source files in Linux using doxygen comments? Mixing different documentation styles can easily become a big mess, because you can't generate external documentation consistently for the whole tree.

Thanks Alex,

Kim
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/