From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7075B128361 for ; Tue, 16 Apr 2024 11:49:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713268172; cv=none; b=Bn5aAxpmz24xCpp0YahUgKhjFsdvdOsINJE+XWtBWwMpAwzIJcjx5J7/kyen3kKtqMwzlyIzri9n6Hy9aW7dHBbV1hc3n0eTGOCmM74pXQFxGFQ4znlzcancQiz/TmtWOsjzRoHBPN/VIW6gCFpmu85vTGBKzFpHCko1PlGXHRY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713268172; c=relaxed/simple; bh=tqExM0tvwgYYvzfoeJzUHezqGwF85pfqg2BcHGHTOAo=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=nAbbjodceyBw/Fm2NxptPQpiphQlUJtjvmzCeF8gDYcnYFW0bXWtTMXgfwndhFmQbfzKCZzt1Fnd04o48/PgoWbckv8jG8OHBpyMN7437naVROVYZkfDs+vWCStW+VnZX2f3hC4OjUf6lMKTzvGQPY46cdptvpRqds6nv9WxGoY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=B2GhDjJL; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="B2GhDjJL" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0410DC113CE; Tue, 16 Apr 2024 11:49:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1713268172; bh=tqExM0tvwgYYvzfoeJzUHezqGwF85pfqg2BcHGHTOAo=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=B2GhDjJLW2WKUr/G74uTDMsCOlAFq0GOIyYwsDvCLJ45tDkSPjLE4pYjl8NPTVc0K rMH05AdS1+1r2r0j0n7AerWzyotq6HJRQqCinxKQeIkEnZJkiTqjLJOEPDrXGIbxVH ehuNKSjGJ7ndXpnTjrC83R59ahZbnO2EHyJ+dj3oUb3jAPNMIMWcL53f4lSOSH9AO0 +inXRo2ZXX5R8ouaA1/Ki/ZE8ObSjcnEzm725uN7eu3GxzH2wfPliyWa1o7X3buNuN h3O67lF4nVpB8RM4D73X/jOjY1YPuTMC1GW5njV095NPChqxu1o/pgCA00pMX7AyTT oh3pWpMVNwqZQ== Date: Tue, 16 Apr 2024 13:49:27 +0200 From: Niklas Cassel To: Manivannan Sadhasivam Cc: Lorenzo Pieralisi , Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= , Rob Herring , Bjorn Helgaas , Heiko Stuebner , Damien Le Moal , linux-pci@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-rockchip@lists.infradead.org Subject: Re: [PATCH] PCI: dw-rockchip: Fix GPIO initialization flag Message-ID: References: <20240327152531.814392-1-cassel@kernel.org> <20240416112807.GC2454@thinkpad> Precedence: bulk X-Mailing-List: linux-pci@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240416112807.GC2454@thinkpad> On Tue, Apr 16, 2024 at 04:58:07PM +0530, Manivannan Sadhasivam wrote: > On Wed, Mar 27, 2024 at 04:25:31PM +0100, Niklas Cassel wrote: > > PERST is active low according to the PCIe specification. > > > > However, the existing pcie-dw-rockchip.c driver does: > > gpiod_set_value(..., 0); msleep(100); gpiod_set_value(..., 1); > > When asserting + deasserting PERST. > > > > This is of course wrong, but because all the device trees for this > > compatible string have also incorrectly marked this GPIO as ACTIVE_HIGH: > > $ git grep -B 10 reset-gpios arch/arm64/boot/dts/rockchip/rk3568* > > $ git grep -B 10 reset-gpios arch/arm64/boot/dts/rockchip/rk3588* > > > > The actual toggling of PERST is correct. > > (And we cannot change it anyway, since that would break device tree > > compatibility.) > > > > However, this driver does request the GPIO to be initialized as > > GPIOD_OUT_HIGH, which does cause a silly sequence where PERST gets > > toggled back and forth for no good reason. > > > > Fix this by requesting the GPIO to be initialized as GPIOD_OUT_LOW > > (which for this driver means PERST asserted). > > > > This will avoid an unnecessary signal change where PERST gets deasserted > > (by devm_gpiod_get_optional()) and then gets asserted > > (by rockchip_pcie_start_link()) just a few instructions later. > > > > Before patch, debug prints on EP side, when booting RC: > > [ 845.606810] pci: PERST asserted by host! > > [ 852.483985] pci: PERST de-asserted by host! > > [ 852.503041] pci: PERST asserted by host! > > [ 852.610318] pci: PERST de-asserted by host! > > > > After patch, debug prints on EP side, when booting RC: > > [ 125.107921] pci: PERST asserted by host! > > [ 132.111429] pci: PERST de-asserted by host! > > > > Without this change, there is no guarantee that PERST will be asserted > > while the core is performing a fundamental reset. > There is no 'core' here, are you referring to the device? If you at pcie-qcom.c, it does: 1) PERST# assert 2) core reset (using reset_control_assert() in ops->init()) 3) PERST# deassert So the EP is held in reset while the RC resets. Right now, for dw-rockchip driver, there is no guarantee that EP is held in reset when the core on RC side resets, which seems bad. > > > (E.g. if the bootloader would leave PERST deasserted.) > > > > I don't follow this last sentence. But even without that, the commit message > itself is descriptive enough. When I flash u-boot on my board, and boot using TFTP, I can see that when u-boot jumps to Linux, PERST# is not asserted and will not be asserted when PCIe RC driver loads. So the scenario mentioned above can happen. (If I don't boot using TFTP, PERST# is deasserted when PCIe RC driver loads.) Anyway, I will remove or clarify this sentence. > > > Signed-off-by: Niklas Cassel > > This is a legitimate bug fix. So you should add the fixes tag and CC stable to > get it backported. Ok, will do in V2. > > But the patch itself looks fine to me. > > Reviewed-by: Manivannan Sadhasivam Thank you. Kind regards, Niklas