From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jaehoon Chung Subject: Re: [PATCH v5 4/9] mmc: dw_mmc: lookup for optional biu and ciu clocks Date: Fri, 31 Aug 2012 15:02:20 +0900 Message-ID: <5040536C.30407@samsung.com> References: <1346237295-7116-1-git-send-email-thomas.abraham@linaro.org> <1346237295-7116-5-git-send-email-thomas.abraham@linaro.org> <503F28E7.1060608@samsung.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-reply-to: Sender: linux-samsung-soc-owner@vger.kernel.org To: Thomas Abraham Cc: Jaehoon Chung , linux-mmc@vger.kernel.org, devicetree-discuss@lists.ozlabs.org, will.newton@imgtec.com, cjb@laptop.org, grant.likely@secretlab.ca, rob.herring@calxeda.com, linux-samsung-soc@vger.kernel.org, kgene.kim@samsung.com, girish.shivananjappa@linaro.org, tgih.jun@samsung.com, patches@linaro.org List-Id: devicetree@vger.kernel.org On 08/31/2012 02:29 PM, Thomas Abraham wrote: > On 30 August 2012 14:18, Jaehoon Chung wrote: >> Hi Thomas, >> >> On 08/29/2012 07:48 PM, Thomas Abraham wrote: >>> Some platforms allow for clock gating and control of bus interface unit clock >>> and card interface unit clock. Add support for clock lookup of optional biu >>> and ciu clocks for clock gating and clock speed determination. >>> >>> Signed-off-by: Abhilash Kesavan >>> Signed-off-by: Thomas Abraham >>> Acked-by: Will Newton >>> --- >>> drivers/mmc/host/dw_mmc.c | 42 +++++++++++++++++++++++++++++++++++++++--- >>> include/linux/mmc/dw_mmc.h | 4 ++++ >>> 2 files changed, 43 insertions(+), 3 deletions(-) >>> >>> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c >>> index 227c42e..90c7c7b 100644 >>> --- a/drivers/mmc/host/dw_mmc.c >>> +++ b/drivers/mmc/host/dw_mmc.c >>> @@ -1960,18 +1960,38 @@ int dw_mci_probe(struct dw_mci *host) >>> return -ENODEV; >>> } >>> >>> - if (!host->pdata->bus_hz) { >>> + host->biu_clk = clk_get(host->dev, "biu"); >>> + if (IS_ERR(host->biu_clk)) >>> + dev_dbg(host->dev, "biu clock not available\n"); >>> + else >>> + clk_prepare_enable(host->biu_clk); >> biu is clock for bus interface? >> if didn't get "biu_clk" or didn't clk_prepare_enable(), then can we initialize the card? > > Hi Jaehoon, > > Yes, the biu clock is for bus interface. The biu and ciu clock lookup > and enable here is optional in the above change. If a platform does > not define these clocks, then the platform code is responsible for > enabling these clocks. If biu_clk is presented... Is there no probability that clk_prepare_enable is failed? > >>> + >>> + host->ciu_clk = clk_get(host->dev, "ciu"); >>> + if (IS_ERR(host->ciu_clk)) >>> + dev_dbg(host->dev, "ciu clock not available\n"); >>> + else >>> + clk_prepare_enable(host->ciu_clk); >>> + >>> + if (IS_ERR(host->ciu_clk)) >>> + host->bus_hz = host->pdata->bus_hz; >>> + else >>> + host->bus_hz = clk_get_rate(host->ciu_clk); >> if clk_get_rate() is incorrect value(ex,400MHz), >> then mmc->f_min value is too high. >> because mmc->f_min is assigned to DIV_ROUND_UP(host->bus_hz, 510) into dw_mc_init_slot. >> Do you have any opinion for solving this? > > One option on Exynos5250 is to use the clock divider in the CLKSEL > register to divide the ciu clock to a lower value. For Exynos4, since > there is no clock divider in CLKSEL register, the platform code should > ensure that the ciu clock has a valid range. I know that can use div-ratio filed at the clksel register. On Exynos5, i known that is used the div-ratio at CLKSEL register. If ciu-clock is 400MHz, host->bus_hz is assigned to 400MHz. 1) host->bus_hz -> 400MHz (at dw-mmc-pltfm.c) 2) mmc->f_min = DIV_ROUND_UP(host->bus_hz, 510) then mmc->f_min is set to 784KHz. 3) then host->bus_hz is re-assigned to value that is divided to div-ratio at CLKSEL register. at this time, host->bus_hz = 100MHz... I think this sequence is something wrong. (Is 784KHz too high for init card?) It's just my thinking..if my understanding is wrong, let me know plz. Best Regards, Jaehoon Chung > > Thanks, > Thomas. > > [...] > -- > To unsubscribe from this list: send the line "unsubscribe linux-mmc" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >