Re: [PATCH v11 01/11] phy: HiSilicon: Add driver for Kirin 970 PCIe PHY

From: Vinod Koul <vkoul@kernel.org>
To: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Cc: Bjorn Helgaas <bhelgaas@google.com>,
	linuxarm@huawei.com, mauro.chehab@huawei.com,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Kishon Vijay Abraham I <kishon@ti.com>,
	Manivannan Sadhasivam <mani@kernel.org>,
	Rob Herring <robh@kernel.org>,
	linux-kernel@vger.kernel.org, linux-phy@lists.infradead.org
Subject: Re: [PATCH v11 01/11] phy: HiSilicon: Add driver for Kirin 970 PCIe PHY
Date: Wed, 18 Aug 2021 15:40:27 +0530	[thread overview]
Message-ID: <YRzck9WqerFtu846@matsya> (raw)
In-Reply-To: <20210818110123.33eba838@coco.lan>

On 18-08-21, 11:01, Mauro Carvalho Chehab wrote:
> Hi Vinod,
> 
> Em Tue, 17 Aug 2021 16:12:37 +0530
> Vinod Koul <vkoul@kernel.org> escreveu:
> 
> > > +	/* FIXME: calling it causes an Asynchronous SError interrupt */
> > > +//	kirin_pcie_clk_ctrl(phy, false);  
> > 
> > when will you fix the fixme and pls remove the deadcode
> 
> Working with clocks on this SoC is very tricky: there are lots of clock
> lines (~70) that are critical for this device to work. Such lines are
> enabled via the Device's firmware, and are supposed to be always
> powered. Powering off such clock lines cause a SError.
> 
> Most clocks on this device are managed by the clk-hikey3670 driver.
> At the current state of clk-hi3670, the only way for HiKey 970
> to even boot is to add:
> 
> 	clk_ignore_unused=true
> 
> as a Kernel boot parameter. That is the solution given by the downstream
> official distributions for HiKey970 at 96boards.
> 
> The fix is to flag the critical clocks with CLK_IS_CRITICAL at the
> clk-hi3670 driver, but finding the right clock set has been a challenge.
> 
> I spent the last couple of weeks trying to identify the critical ones,
> as I'm aiming to be able to use a Kernel built with a default arm64
> one of my goals is to have this device working fine with a
> "make defconfig" Kernel.
> 
> So, I added this patch:
> 
> 	https://lore.kernel.org/lkml/2d2de5e902ced072bcfd5e5311d6b10326b9245b.1627041240.git.mchehab+huawei@kernel.org/
> 
> to my tree (which reduces the set of clocks using CLK_IGNORE_UNUSED
> from 308 to 163 clocks). Than I ran script that was dropping the
> flag one by one, boots the new Kernel and do a sanity check. When it 
> fails to boot, I manually dropped the patch, and re-run the script
> to test the remaining clocks. After a couple of weeks, I reached a patch
> with 78 clock lines that seemed critical, but the resulting patch was
> not stable, as, depending on the day I boot the Kernel with such patch,
> it crashes with SError in a couple of seconds after booting, or 
> cause the Ethernet firmware to not load.
> 
> I intend to keep trying to find the clock lines that can't be disabled,
> but this is very time consuming, as I couldn't find any documentation
> about that. So, it has to be done empirically.
> 
> -
> 
> In any case, fixing it doesn't sound a critical issue for the PHY
> driver. I mean, right now, this patchset allows removing and 
> re-inseting the PCIe driver, which is already an improvement over the
> original upstream driver, which was missing the power-off logic for
> Kirin 960.
> 
> With this patchset, both power-off/power-on logic for both HiKey960
> (where the PHY is inside the pcie-kirin driver) and for HiKey970,
> which uses this PHY driver. On both devices, I tested an endless loop 
> with rmmod/modprobe for the PCIe.
> 
> Besides that, in practice, removing PCIe in runtime is something that
> people usually don't do.
> 
> So, while it would be cool to balance the clock disable logic,
> I don't think this is a critical issue in this particular case.

Okay sounds fair to me, I think fixme should be left but the c99 style
code commented out can be removed

-- 
~Vinod