From: Thierry Reding <thierry.reding@gmail.com>
To: Dmitry Osipenko <digetx@gmail.com>
Cc: linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org,
krzk@kernel.org, jonathanh@nvidia.com,
linux-tegra@vger.kernel.org
Subject: Re: [PATCH v3 1/3] memory: tegra: Add devm_tegra_get_memory_controller()
Date: Wed, 30 Sep 2020 18:15:03 +0200 [thread overview]
Message-ID: <20200930161503.GF3833404@ulmo> (raw)
In-Reply-To: <839df5d6-513f-3d77-ba5f-a1afe5d0883a@gmail.com>
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On Wed, Sep 30, 2020 at 07:06:27PM +0300, Dmitry Osipenko wrote:
> 30.09.2020 19:03, Thierry Reding пишет:
> > On Wed, Sep 30, 2020 at 06:53:06PM +0300, Dmitry Osipenko wrote:
> >> 30.09.2020 18:23, Thierry Reding пишет:
> >>> On Wed, Sep 30, 2020 at 01:42:56AM -0700, Nicolin Chen wrote:
> >>>> From: Dmitry Osipenko <digetx@gmail.com>
> >>>>
> >>>> Multiple Tegra drivers need to retrieve Memory Controller and hence there
> >>>> is quite some duplication of the retrieval code among the drivers. Let's
> >>>> add a new common helper for the retrieval of the MC.
> >>>>
> >>>> Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
> >>>> Signed-off-by: Nicolin Chen <nicoleotsuka@gmail.com>
> >>>> ---
> >>>>
> >>>> Changelog
> >>>> v2->v3:
> >>>> * Replaced with Dimtry's devm_tegra_get_memory_controller()
> >>>> v1->v2:
> >>>> * N/A
> >>>>
> >>>> drivers/memory/tegra/mc.c | 39 +++++++++++++++++++++++++++++++++++++++
> >>>> include/soc/tegra/mc.h | 17 +++++++++++++++++
> >>>> 2 files changed, 56 insertions(+)
> >>>
> >>> Let's not add this helper, please. If a device needs a reference to the
> >>> memory controller, it should have a phandle to the memory controller in
> >>> device tree so that it can be looked up explicitly.
> >>>
> >>> Adding this helper is officially sanctioning that it's okay not to have
> >>> that reference and that's a bad idea.
> >>
> >> And please explain why it's a bad idea, I don't see anything bad here at
> >> all.
> >
> > Well, you said yourself in a recent comment that we should avoid global
> > variables. devm_tegra_get_memory_controller() is nothing but a glorified
> > global variable.
>
> This is not a variable, but a common helper function which will remove
> the duplicated code and will help to avoid common mistakes like a missed
> put_device().
Yeah, you're right: this is actually much worse than a global variable.
It's a helper function that needs 50+ lines in order to effectively
access a global variable.
You could write this much simpler by doing something like this:
static struct tegra_mc *global_mc;
int tegra_mc_probe(...)
{
...
global_mc = mc;
...
}
struct tegra_mc *tegra_get_memory_controller(void)
{
return global_mc;
}
The result is *exactly* the same, except that this is actually more
honest. Nicolin's patch *pretends* that it isn't using a global variable
by wrapping a lot of complicated code around it.
But that doesn't change the fact that this accesses a singleton object
without actually being able to tie it to the device in the first place.
Thierry
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next prev parent reply other threads:[~2020-09-30 16:15 UTC|newest]
Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-30 8:42 [PATCH v3 0/3] iommu/tegra-smmu: Add PCI support Nicolin Chen
2020-09-30 8:42 ` [PATCH v3 1/3] memory: tegra: Add devm_tegra_get_memory_controller() Nicolin Chen
2020-09-30 9:07 ` Krzysztof Kozlowski
2020-09-30 9:41 ` Nicolin Chen
2020-09-30 10:27 ` Krzysztof Kozlowski
2020-09-30 14:41 ` Dmitry Osipenko
2020-09-30 14:45 ` Krzysztof Kozlowski
2020-09-30 15:22 ` Dmitry Osipenko
2020-09-30 15:23 ` Thierry Reding
2020-09-30 15:27 ` Dmitry Osipenko
2020-09-30 15:53 ` Dmitry Osipenko
2020-09-30 16:03 ` Thierry Reding
2020-09-30 16:06 ` Dmitry Osipenko
2020-09-30 16:15 ` Thierry Reding [this message]
2020-09-30 16:26 ` Dmitry Osipenko
2020-09-30 16:38 ` Thierry Reding
2020-09-30 17:32 ` Dmitry Osipenko
2020-09-30 8:42 ` [PATCH v3 2/3] iommu/tegra-smmu: Rework .probe_device and .attach_dev Nicolin Chen
2020-09-30 9:21 ` Krzysztof Kozlowski
2020-09-30 9:40 ` Nicolin Chen
2020-09-30 10:19 ` Krzysztof Kozlowski
2020-09-30 14:41 ` Dmitry Osipenko
2020-09-30 15:09 ` Dmitry Osipenko
2020-09-30 20:51 ` Nicolin Chen
2020-09-30 15:31 ` Thierry Reding
2020-09-30 15:36 ` Dmitry Osipenko
2020-09-30 16:06 ` Thierry Reding
2020-09-30 16:25 ` Dmitry Osipenko
2020-09-30 16:47 ` Thierry Reding
2020-10-01 2:11 ` Dmitry Osipenko
2020-10-01 7:58 ` Thierry Reding
2020-10-01 19:04 ` Dmitry Osipenko
2020-10-05 9:16 ` Thierry Reding
2020-10-05 9:38 ` Dmitry Osipenko
2020-10-05 10:27 ` Thierry Reding
2020-09-30 16:10 ` Thierry Reding
2020-09-30 16:29 ` Dmitry Osipenko
2020-10-01 7:59 ` Thierry Reding
2020-09-30 20:36 ` Nicolin Chen
2020-09-30 21:24 ` Dmitry Osipenko
2020-09-30 21:32 ` Nicolin Chen
2020-09-30 21:56 ` Dmitry Osipenko
2020-10-01 1:26 ` Nicolin Chen
2020-10-01 2:06 ` Dmitry Osipenko
2020-10-01 2:48 ` Nicolin Chen
2020-10-01 4:04 ` Dmitry Osipenko
2020-10-01 10:23 ` Thierry Reding
2020-10-01 11:04 ` Nicolin Chen
2020-10-01 20:33 ` Dmitry Osipenko
2020-10-02 1:07 ` Nicolin Chen
2020-10-02 1:55 ` Dmitry Osipenko
2020-10-02 2:54 ` Nicolin Chen
2020-10-05 7:24 ` Thierry Reding
2020-10-05 7:13 ` Thierry Reding
2020-10-05 8:14 ` Dmitry Osipenko
2020-10-05 9:31 ` Thierry Reding
2020-10-01 9:54 ` Thierry Reding
2020-10-01 9:51 ` Thierry Reding
2020-10-01 10:33 ` Nicolin Chen
2020-10-01 10:42 ` Thierry Reding
2020-10-01 9:47 ` Thierry Reding
2020-10-01 10:46 ` Thierry Reding
2020-10-02 1:29 ` Nicolin Chen
2020-09-30 8:42 ` [PATCH v3 3/3] iommu/tegra-smmu: Add PCI support Nicolin Chen
2020-09-30 14:53 ` Dmitry Osipenko
2020-09-30 20:03 ` Nicolin Chen
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