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[209.85.222.54]) by smtp.gmail.com with ESMTPSA id t193sm6931vkc.48.2019.05.23.11.36.09 for (version=TLS1_3 cipher=AEAD-AES128-GCM-SHA256 bits=128/128); Thu, 23 May 2019 11:36:09 -0700 (PDT) Received: by mail-ua1-f54.google.com with SMTP id 49so2573180uas.0 for ; Thu, 23 May 2019 11:36:09 -0700 (PDT) X-Received: by 2002:ab0:4a97:: with SMTP id s23mr320550uae.19.1558636568655; Thu, 23 May 2019 11:36:08 -0700 (PDT) MIME-Version: 1.0 References: <20190501043734.26706-1-bjorn.andersson@linaro.org> <20190501043734.26706-3-bjorn.andersson@linaro.org> <5ce6e0cd.1c69fb81.9a03e.0260@mx.google.com> In-Reply-To: <5ce6e0cd.1c69fb81.9a03e.0260@mx.google.com> From: Doug Anderson Date: Thu, 23 May 2019 11:35:55 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v7 2/4] soc: qcom: Add AOSS QMP driver To: Stephen Boyd Cc: Bjorn Andersson , Andy Gross , David Brown , Rob Herring , Mark Rutland , linux-arm-msm , devicetree@vger.kernel.org, LKML Content-Type: text/plain; charset="UTF-8" Sender: linux-arm-msm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-arm-msm@vger.kernel.org Hi, On Thu, May 23, 2019 at 11:05 AM Stephen Boyd wrote: > > Quoting Doug Anderson (2019-05-23 09:38:13) > > Hi, > > > > On Tue, Apr 30, 2019 at 9:38 PM Bjorn Andersson > > wrote: > > > > > +static int qmp_qdss_clk_add(struct qmp *qmp) > > > +{ > > > + struct clk_init_data qdss_init = { > > > + .ops = &qmp_qdss_clk_ops, > > > + .name = "qdss", > > > + }; > > > > Can't qdss_init be "static const"? That had the advantage of not > > needing to construct it on the stack and also of it having a longer > > lifetime. It looks like clk_register() stores the "hw" pointer in its > > structure and the "hw" structure will have a pointer here. While I > > can believe that it never looks at it again, it's nice if that pointer > > doesn't point somewhere on an old stack. > > > > I suppose we could go the other way and try to mark more stuff in this > > module as __init and __initdata, but even then at least the pointer > > won't be onto a stack. ;-) > > > > Const would be nice, but otherwise making it static isn't a good idea. Even aside from the whole "not having it store a pointer to the stack", "static const" is likely to reduce overall memory consumption / number of instructions by a tiny bit because we don't need to copy this structure onto the stack--we can just use it in place. As written (or by just adding const but not static const): qmp_probe() is 1840 bytes long. ...and has this snippet: 0xffffff80084a58d4 <+1152>: adrp x1, 0xffffff8008a5b000 0xffffff80084a58d8 <+1156>: add x1, x1, #0x600 0xffffff80084a58dc <+1160>: add x0, sp, #0x10 0xffffff80084a58e0 <+1164>: mov w2, #0x28 // #40 0xffffff80084a58e4 <+1168>: add x22, sp, #0x10 0xffffff80084a58e8 <+1172>: bl 0xffffff800896e800 With this as static const: qmp_probe is 1820 bytes long. ...and has this snippet: 0xffffff80084a58dc <+1160>: adrp x8, 0xffffff8008a5b000 0xffffff80084a58e0 <+1164>: add x8, x8, #0x550 > The clk_init_data structure is all copied over, although we do leave a > dangling pointer to it stored inside the clk_hw structure we don't use > it after clk registration. Maybe we should overwrite the pointer with > NULL once we're done in clk_register() so that clk providers can't use > it. It might break somebody but would at least clarify this point. Setting it to NULL seems like it would be a good idea. Now that I think on it I believe I've actually tripped over this before trying to read the '.name' from here... :-P > > > +static void qmp_pd_remove(struct qmp *qmp) > > > +{ > > > + struct genpd_onecell_data *data = &qmp->pd_data; > > > + struct device *dev = qmp->dev; > > > + int i; > > > + > > > + of_genpd_del_provider(dev->of_node); > > > + > > > + for (i = 0; i < data->num_domains; i++) > > > + pm_genpd_remove(data->domains[i]); > > > > Still feels like the above loop would be better as: > > for (i = data->num_domains - 1; i >= 0; i--) > > > > Reason being to remove in reverse order? Otherwise this looks like an > opinion. 1. Matches the order of the error handling case above (see unroll_genpds label) 2. In general you avoid more unexpected problems by un-initting in the reverse order you initted. -Doug