You have to modify in the following file in the yocto build to enable preset value:
tmp/work-shared/<board>/kernel-source/drivers/mmc/host/sdhci.c The following function does the enabling of preset value: static void sdhci_enable_preset_value(struct sdhci_host *host, bool enable) { u16 ctrl; /* Host Controller v3.00 defines preset value registers */ if (host->version < SDHCI_SPEC_300) return; ctrl = sdhci_readw(host, SDHCI_HOST_CONTROL2); /* * We only enable or disable Preset Value if they are not already * enabled or disabled respectively. Otherwise, we bail out. */ if (enable && !(ctrl & SDHCI_CTRL_PRESET_VAL_ENABLE)) { ctrl |= SDHCI_CTRL_PRESET_VAL_ENABLE; sdhci_writew(host, ctrl, SDHCI_HOST_CONTROL2); host->flags |= SDHCI_PV_ENABLED; } else if (!enable && (ctrl & SDHCI_CTRL_PRESET_VAL_ENABLE)) { ctrl &= ~SDHCI_CTRL_PRESET_VAL_ENABLE; sdhci_writew(host, ctrl, SDHCI_HOST_CONTROL2); host->flags &= ~SDHCI_PV_ENABLED; } } The function can be called in the following way: sdhci_enable_preset_value(host, true); Thanks, Juinee From: meta-intel-boun...@yoctoproject.org [mailto:meta-intel-boun...@yoctoproject.org] On Behalf Of Francesco Camarda (fcamarda) Sent: Tuesday, August 8, 2017 6:24 PM To: meta-intel@yoctoproject.org Subject: [meta-intel] change hostctrl2_presetvalueenable default value Hi, >From of the Apollo Lake SoC External Design Specification (EDS) Volume 2 of >3<https://embedded.communities.intel.com/external-link.jspa?url=https%3A%2F%2Fedc.intel.com%2FLink.aspx%3Fid%3D14201> > document # 557556 (on pages from 4511 to 4515) it is possible to change the >driver strength that depends on the setting of bit 15 >(hostctrl2_presetvalueenable). If Preset Value Enable = 0, the driver strength is set by the host driver. If Preset Value Enable = 1, the driver strength is automatically set to the values specified in the Capabilities Register (capabilities)-Offset 40h (refer also to Capabilities Register (capabilities)-Offset 40h). Which of the file of the build (EC31) I should modify to put the Preset Value Enable = 1? Thanks & Regards, Francesco
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