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Mon, 01 Apr 2019 01:40:22 -0700 (PDT) Message-ID: <63fc525faf2d82cb2436a17ab2206293aeef6c31.camel@baylibre.com> Subject: Re: [PATCH 1/3] clk: meson: mpll: properly handle spread spectrum From: Jerome Brunet To: Martin Blumenstingl Date: Mon, 01 Apr 2019 10:40:20 +0200 In-Reply-To: References: <20190329153325.23869-1-jbrunet@baylibre.com> <20190329153325.23869-2-jbrunet@baylibre.com> <3bef1bb26e9eff0cfc20cd4bb78a5d7cea4c5076.camel@baylibre.com> User-Agent: Evolution 3.30.5 (3.30.5-1.fc29) MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190401_014024_684858_C74454F5 X-CRM114-Status: GOOD ( 25.48 ) X-BeenThere: linux-amlogic@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-amlogic@lists.infradead.org, linux-clk@vger.kernel.org, linux-kernel@vger.kernel.org, Neil Armstrong Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-amlogic" Errors-To: linux-amlogic-bounces+linux-amlogic=archiver.kernel.org@lists.infradead.org On Sat, 2019-03-30 at 16:56 +0100, Martin Blumenstingl wrote: > Hi Jerome, > > On Sat, Mar 30, 2019 at 12:07 AM Jerome Brunet wrote: > > On Fri, 2019-03-29 at 20:39 +0100, Martin Blumenstingl wrote: > > > Hi Jerome, > > > > > > On Fri, Mar 29, 2019 at 4:34 PM Jerome Brunet wrote: > > > > The bit 'SSEN' available on some MPLL DSS outputs is not related to the > > > > fractional part of the divider but to the function called > > > > 'Spread Spectrum'. > > > > > > > > This function might be used to solve EM issues by adding a jitter on > > > > clock signal. This widens the signal spectrum and weakens the peaks in it. > > > > > > > > While spread spectrum might be useful for some application, it is > > > > problematic for others, such as audio. > > > > > > > > This patch introduce a new flag to the MPLL driver to enable (or not) the > > > > spread spectrum function. > > > > > > > > Fixes: 1f737ffa13ef ("clk: meson: mpll: fix mpll0 fractional part ignored") > > > > Signed-off-by: Jerome Brunet > > > > --- > > > > drivers/clk/meson/clk-mpll.c | 9 ++++++--- > > > > drivers/clk/meson/clk-mpll.h | 1 + > > > > 2 files changed, 7 insertions(+), 3 deletions(-) > > > > [...] > > > > Yes, none of our application require spread spectrum > thank you for the explanation. can you please add it to the patch description? I think I described spread spectrum already in the commit description. > > > The fact is that only 2 MPLL had this bit, mpll0 on gx (without effect) and > > mpll0 on axg: actually spread spectrum impacts mpll2, making it unusable, as > > explained in the related patch > > > > > based on the original commit 1f737ffa13ef ("clk: meson: mpll: fix > > > mpll0 fractional part ignored") it seems that > > > CLK_MESON_MPLL_SPREAD_SPECTRUM should be set for mpll0 (at least on > > > GXBB and Meson8b) > > > > > > > There a patch specifically targeting gxbb. > I missed that, sorry for the noise > > > I have checked on GXL and this bit had no effect (fractional part still on, no > > spread spectrum) > > > > So either we fixed something since then or I messed up when doing the patch > > initially. > > > > Feel free to cross check > I tried it on Meson8b and it seems that there's no difference. I've > done a bit of software archaeology: > $ grep -R mpll_cntl uboot-2015-01-15-23a3562521/ | grep "=" | head -n3 > uboot-2015-01-15-23a3562521/board/amlogic/m8_k100_1G/firmware/timming.c: > .mpll_cntl = 0x600009A9, //2.5G, fixed > uboot-2015-01-15-23a3562521/board/amlogic/m8_k100_2G/firmware/timming.c: > .mpll_cntl = 0x600009A9, //2.5G, fixed > uboot-2015-01-15-23a3562521/board/amlogic/m8b_ft_v1/firmware/timming.c: > .mpll_cntl = 0x600009A9, //2.5G, fixed > > Ethernet is still working on my Odroid-C1, so you can add my: > Tested-by: Martin Blumenstingl > > > Regards > Martin _______________________________________________ linux-amlogic mailing list linux-amlogic@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-amlogic