Re: [PATCH 1/4] drivers/bus: Added Freescale Management Complex APIs
From: German Rivera
Date: Thu Sep 18 2014 - 23:05:17 EST
On 09/18/2014 03:22 PM, Kim Phillips wrote:
On Thu, 18 Sep 2014 15:14:03 +0200
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.
I will refactor this function to use devm_ functions, to simplify the
error cleanup logic as you suggested, but still keep the current
signature of the function, as I don't think it is a good practice
to just return NULL in case of error, hiding the actual cause of the
error. Also, mixing returning a valid pointer and an error encoded
as an invalid pointer is not clean and can be error-prone for callers,
if some caller just checks for NULL instead of using IS_ERR() ir
IS_ERR_OR_NULL().
+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.
Having an extra pass-by-reference argument does not make the code
that complicated. Bit more importantly the simplicity that you gain
by not using the extra pass-by-reference pointer comes at the price
of making the interface less safer to use (more error-prone
for the caller as I mentioned above), which I think it is a bad trade off.
+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.
All this will be gone with the refactoring to use devm_ APIs.
+ 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?
In this particular case, this comment doe snot apply anymore, as
the magic filed will be removed.
+/**
+ * @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.
As I mentioned in the reply to Alex, I will remove the minor version check.
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