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[109.252.192.57]) by smtp.googlemail.com with ESMTPSA id y24sm1522328ljm.125.2021.01.17.15.39.37 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 17 Jan 2021 15:39:37 -0800 (PST) Subject: Re: [PATCH v1 2/5] ALSA: hda/tegra: Reset hardware To: Thierry Reding Cc: Jonathan Hunter , Sameer Pujar , Peter Geis , Nicolas Chauvet , Takashi Iwai , Jaroslav Kysela , alsa-devel@alsa-project.org, linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org References: <20210112125834.21545-1-digetx@gmail.com> <20210112125834.21545-3-digetx@gmail.com> From: Dmitry Osipenko Message-ID: Date: Mon, 18 Jan 2021 02:39:37 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.4.2 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 15.01.2021 18:35, Thierry Reding пишет: > On Tue, Jan 12, 2021 at 03:58:31PM +0300, Dmitry Osipenko wrote: >> Reset hardware in order to bring it into a predictable state. >> >> Tested-by: Peter Geis >> Tested-by: Nicolas Chauvet >> Signed-off-by: Dmitry Osipenko >> --- >> sound/pci/hda/hda_tegra.c | 18 ++++++++++++++++++ >> 1 file changed, 18 insertions(+) >> >> diff --git a/sound/pci/hda/hda_tegra.c b/sound/pci/hda/hda_tegra.c >> index 4c799661c2f6..e406b7980f31 100644 >> --- a/sound/pci/hda/hda_tegra.c >> +++ b/sound/pci/hda/hda_tegra.c >> @@ -17,6 +17,7 @@ >> #include >> #include >> #include >> +#include >> #include >> #include >> #include >> @@ -70,6 +71,7 @@ >> struct hda_tegra { >> struct azx chip; >> struct device *dev; >> + struct reset_control *reset; >> struct clk_bulk_data clocks[3]; >> unsigned int nclocks; >> void __iomem *regs; >> @@ -167,6 +169,12 @@ static int __maybe_unused hda_tegra_runtime_resume(struct device *dev) >> struct hda_tegra *hda = container_of(chip, struct hda_tegra, chip); >> int rc; >> >> + if (!(chip && chip->running)) { > > Isn't that check for !chip a bit redundant? If that pointer isn't valid, > we're just going to go crash when dereferencing hda later on, so I think > this can simply be: > > if (!chip->running) > > I guess you took this from the inverse check below, but I think we can > also drop it from there, perhaps in a separate patch. > >> + rc = reset_control_assert(hda->reset); >> + if (rc) >> + return rc; >> + } >> + >> rc = clk_bulk_prepare_enable(hda->nclocks, hda->clocks); >> if (rc != 0) >> return rc; >> @@ -176,6 +184,10 @@ static int __maybe_unused hda_tegra_runtime_resume(struct device *dev) >> /* disable controller wake up event*/ >> azx_writew(chip, WAKEEN, azx_readw(chip, WAKEEN) & >> ~STATESTS_INT_MASK); >> + } else { >> + rc = reset_control_reset(hda->reset); > > The "if (chip)" part definitely doesn't make sense after this anymore > because now if chip == NULL, then we end up in here and dereference an > invalid "hda" pointer. Okay, I took a note for the v3. > Also, why reset_control_reset() here? We'll reach this if we ran > reset_control_assert() above, so this should just be > reset_control_deassert() to undo that, right? I suppose it wouldn't hurt > to put throw that standard usleep_range() in there as well that we use > to wait between reset assert and deassert to make sure the clocks have > stabilized and the reset has indeed propagated through the whole IP. The reset_control_reset() does the delaying before the deassert, i.e. it does assert -> udelay(1) -> deassert. https://elixir.free-electrons.com/linux/v5.11-rc3/source/drivers/clk/tegra/clk.c#L133 The reset_control_reset() usage appears to be a bit more code-tidy variant in comparison to delaying directly. But I don't mind to use delay + reset_control_deassert() directly since it may not be obvious to everyone what reset_control_reset() does. I'll change it in v3.