From mboxrd@z Thu Jan 1 00:00:00 1970 From: cang@codeaurora.org Subject: Re: [PATCH 1/1] scsi: ufs: make UFS Tx lane1 clock optional Date: Wed, 10 Oct 2018 21:46:33 +0800 Message-ID: <36c6c1a95ff396ac108501f9fe76ef65@codeaurora.org> References: <1538973275-5961-1-git-send-email-cang@codeaurora.org> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Doug Anderson Cc: subhashj@codeaurora.org, Asutosh Das , Vivek Gautam , Rajendra Nayak , Evan Green , Vinayak Holikatti , jejb@linux.vnet.ibm.com, "Martin K. Petersen" , linux-scsi@vger.kernel.org, venkatg@codeaurora.org, LKML List-Id: linux-scsi@vger.kernel.org Hi Doug, Really thank you for your review. On 2018-10-10 05:56, Doug Anderson wrote: > Hi, > > On Sun, Oct 7, 2018 at 9:34 PM Can Guo wrote: >> >> From: Venkat Gopalakrishnan >> >> The UFS Tx lane1 clock could be muxed, hence keep it optional by >> ignoring >> it if it is not provided in device tree. > > Thanks for the updated commit message. This makes much more sense now! > :-) > > Yeah, sorry for making you guys confused. My bad previously. >> @@ -113,10 +110,10 @@ static void ufs_qcom_disable_lane_clks(struct >> ufs_qcom_host *host) >> if (!host->is_lane_clks_enabled) >> return; >> >> - if (host->hba->lanes_per_direction > 1) >> + if (host->tx_l1_sync_clk) >> clk_disable_unprepare(host->tx_l1_sync_clk); > > I don't believe you need the "if". A NULL clock is by definition OK > to enable / disable which is designed to make optional clocks easier > to deal with. > > You are right, I checked the implemention, clock enable/disable func would bail out if clk is NULL just as your comments. >> clk_disable_unprepare(host->tx_l0_sync_clk); >> - if (host->hba->lanes_per_direction > 1) >> + if (host->rx_l1_sync_clk) >> clk_disable_unprepare(host->rx_l1_sync_clk); > > optional: Technically this part of the patch wasn't actually needed, > right? "rx_l1_sync_clk" is not optional so that means that > "rx_l1_sync_clk" should be non-NULL exactly when lanes_per_direction > > 1. > > ...but actually I'm fine with keeping this part of your patch for > symmetry. Especially since you can leverage the > clk_disable_unprepare(NULL) to simplify your code. Please mention in > your commit message that this is a cleanup and just for symmetry. > Probably also remove the "if" tests that are guarding > ufs_qcom_host_clk_enable(). > > Sure, got it. >> clk_disable_unprepare(host->rx_l0_sync_clk); >> >> @@ -141,24 +138,21 @@ static int ufs_qcom_enable_lane_clks(struct >> ufs_qcom_host *host) >> if (err) >> goto disable_rx_l0; >> >> - if (host->hba->lanes_per_direction > 1) { >> + if (host->rx_l1_sync_clk) { > > Similar: the above change isn't required but I'm OK if you want to > make this change for symmetry / to cleanup clock handling. Please > mention in your commit message. > > Sure, shall do so. >> + /* The tx lane1 clk could be muxed, hence keep this optional >> */ >> + if (host->tx_l1_sync_clk) >> + ufs_qcom_host_clk_enable(dev, "tx_lane1_sync_clk", >> + host->tx_l1_sync_clk); > > If "host->tx_l1_sync_clk" is provided then you should still check the > return value of ufs_qcom_host_clk_enable(), right? ...so please leave > the error path here. > > Yeah... you are right. >> @@ -174,23 +168,33 @@ static int ufs_qcom_init_lane_clks(struct >> ufs_qcom_host *host) >> >> err = ufs_qcom_host_clk_get(dev, >> "rx_lane0_sync_clk", &host->rx_l0_sync_clk); >> - if (err) >> + if (err) { >> + dev_err(dev, "%s: failed to get rx_lane0_sync_clk, err >> %d", >> + __func__, err); > > nit: including "__func__" in dev_xxx() calls is discouraged. The > "dev_xxx" calls already print the device name and the string within a > given device driver should be unique enough so __func__ just adds crap > to the logs. If you really feel that __func__ adds something for you, > try posting up a patch to make all "dev_err" functions include > __func__. ...but I think you'd probably be rejected. > > suggestion: you'd save a few lines of code and simplify your probe if > you just passed an "optional" bool to the ufs_qcom_host_clk_get() that > controlled the printout. > > Good idea! >> - err = ufs_qcom_host_clk_get(dev, "tx_lane1_sync_clk", >> - &host->tx_l1_sync_clk); >> + /* The tx lane1 clk could be muxed, hence keep this >> optional */ >> + ufs_qcom_host_clk_get(dev, "tx_lane1_sync_clk", >> + &host->tx_l1_sync_clk); > > To be technically correct you should actually check the error value > returned by ufs_qcom_host_clk_get(). Specifically figure out what the > error value is when "tx_lane1_sync_clk" isn't specified and check for > that. > > ...one reason this matters is -EPROBE_DEFER. In theory devm_clk_get() > could return -EPROBE_DEFER. In such a case you'd want to exit the > probe, not continue on. It's also just good coding practice to handle > just the error you want though so that if the function returned some > other failing case you'd propagate it down instead of eating it. > > If you passed "optional" to ufs_qcom_host_clk_get() as suggested above > you could put this error-code checking in ufs_qcom_host_clk_get() and > return 0 from that function if an optional clock was found to not > exist. > > -Doug I think I understand it. Thanks a lot for the thorough review and suggestions. -Can Guo