RE: [PATCH v4 2/2] misc: xlnx_vcu: Add Xilinx ZYNQMP VCU logicoreIP init driver

[Dhaval Rajeshbhai Shah <DSHAH@xilinx.com>]

Hi Randy,

Thanks a lot for the review.

> -----Original Message-----
> From: Randy Dunlap [mailto:rdunlap@infradead.org]
> Sent: Saturday, December 16, 2017 2:18 PM
> To: Dhaval Rajeshbhai Shah <DSHAH@xilinx.com>; arnd@arndb.de;
> gregkh@linuxfoundation.org; robh+dt@kernel.org; mark.rutland@arm.com
> Cc: devicetree@vger.kernel.org; linux-kernel@vger.kernel.org;
> michal.simek@xilinx.com; Hyun Kwon <hyunk@xilinx.com>; Dhaval Rajeshbhai
> Shah <DSHAH@xilinx.com>
> Subject: Re: [PATCH v4 2/2] misc: xlnx_vcu: Add Xilinx ZYNQMP VCU logicoreIP
> init driver
> 
> On 12/14/2017 11:24 PM, Dhaval Shah wrote:
> > Xilinx ZYNQMP logicoreIP Init driver is based on the new LogiCoreIP
> > design created. This driver provides the processing system and
> > programmable logic isolation. Set the frequency based on the clock
> > information get from the logicoreIP register set.
> >
> > It is put in drivers/misc as there is no subsystem for this logicoreIP.
> >
> > Signed-off-by: Dhaval Shah <dshah@xilinx.com>
> > ---
> >
> >  drivers/misc/Kconfig    |  15 ++
> >  drivers/misc/Makefile   |   1 +
> >  drivers/misc/xlnx_vcu.c | 631
> > ++++++++++++++++++++++++++++++++++++++++++++++++
> >  3 files changed, 647 insertions(+)
> >  create mode 100644 drivers/misc/xlnx_vcu.c
> 
> > diff --git a/drivers/misc/xlnx_vcu.c b/drivers/misc/xlnx_vcu.c new
> > file mode 100644 index 0000000..f489d34
> > --- /dev/null
> > +++ b/drivers/misc/xlnx_vcu.c
> > @@ -0,0 +1,631 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Xilinx VCU Init
> > + *
> > + * Copyright (C) 2016 - 2017 Xilinx, Inc.
> > + *
> > + * Contacts   Dhaval Shah <dshah@xilinx.com>
> > + */
> > +#include <linux/clk.h>
> > +#include <linux/device.h>
> > +#include <linux/errno.h>
> > +#include <linux/io.h>
> > +#include <linux/module.h>
> > +#include <linux/of_platform.h>
> > +#include <linux/platform_device.h>
> 
> [snip]
> 
> 
> > +/**
> > + * xvcu_set_vcu_pll_info - Set the VCU PLL info
> > + * @xvcu:	Pointer to the xvcu_device structure
> > + *
> > + * Programming the VCU PLL based on the user configuration
> > + * (ref clock freq, core clock freq, mcu clock freq).
> > + * Core clock frequency has higher priority than mcu clock frequency
> > + * Errors in following cases
> > + *    - When mcu or clock clock get from logicoreIP is 0
> > + *    - When VCU PLL DIV related bits value other than 1
> > + *    - When proper data not found for given data
> > + *    - When sis570_1 clocksource related operation failed
> > + *
> > + * Return:	Returns status, either success or error+reason
> > + */
> > +static int xvcu_set_vcu_pll_info(struct xvcu_device *xvcu) {
> > +	u32 refclk, coreclk, mcuclk, inte, deci;
> > +	u32 divisor_mcu, divisor_core, fvco;
> > +	u32 clkoutdiv, vcu_pll_ctrl, pll_clk;
> > +	u32 cfg_val, mod, ctrl;
> > +	int ret;
> > +	unsigned int i;
> > +	const struct xvcu_pll_cfg *found = NULL;
> > +
> > +	inte = xvcu_read(xvcu->logicore_reg_ba, VCU_PLL_CLK);
> > +	deci = xvcu_read(xvcu->logicore_reg_ba, VCU_PLL_CLK_DEC);
> > +	coreclk = xvcu_read(xvcu->logicore_reg_ba, VCU_CORE_CLK) * MHZ;
> > +	mcuclk = xvcu_read(xvcu->logicore_reg_ba, VCU_MCU_CLK) * MHZ;
> > +	if (!mcuclk || !coreclk) {
> > +		dev_err(xvcu->dev, "Invalid mcu and core clock data\n");
> > +		return -EINVAL;
> > +	}
> > +
> > +	refclk = (inte * MHZ) + (deci * (MHZ / FRAC));
> > +	dev_dbg(xvcu->dev, "Ref clock from logicoreIP is %uHz\n", refclk);
> > +	dev_dbg(xvcu->dev, "Core clock from logicoreIP is %uHz\n", coreclk);
> > +	dev_dbg(xvcu->dev, "Mcu clock from logicoreIP is %uHz\n", mcuclk);
> > +
> > +	clk_disable_unprepare(xvcu->pll_ref);
> > +	ret = clk_set_rate(xvcu->pll_ref, refclk);
> > +	if (ret)
> > +		dev_warn(xvcu->dev, "failed to set logicoreIP refclk rate\n");
> > +
> > +	ret = clk_prepare_enable(xvcu->pll_ref);
> > +	if (ret) {
> > +		dev_err(xvcu->dev, "failed to enable pll_ref clock source\n");
> > +		return ret;
> > +	}
> > +
> > +	refclk = clk_get_rate(xvcu->pll_ref);
> > +
> > +	/*
> > +	 * The divide-by-2 should be always enabled (==1)
> > +	 * to meet the timing in the design.
> > +	 * Otherwise, it's an error
> > +	 */
> > +	vcu_pll_ctrl = xvcu_read(xvcu->vcu_slcr_ba, VCU_PLL_CTRL);
> > +	clkoutdiv = vcu_pll_ctrl >> VCU_PLL_CTRL_CLKOUTDIV_SHIFT;
> > +	clkoutdiv = clkoutdiv && VCU_PLL_CTRL_CLKOUTDIV_MASK;
> > +	if (clkoutdiv != 1) {
> > +		dev_err(xvcu->dev, "clkoutdiv value is invalid\n");
> > +		return -EINVAL;
> > +	}
> > +
> > +	for (i = ARRAY_SIZE(xvcu_pll_cfg) - 1; i > 0; i--) {
> 
> When does that for loop terminate?
> 
This loop will terminate either it reach to i =0 and one other case is when it find the proper expected value.  Break statement is used to exit in that case. 
> > +		const struct xvcu_pll_cfg *cfg = &xvcu_pll_cfg[i];
> > +
> > +		fvco = cfg->fbdiv * refclk;
> > +		if (fvco >= FVCO_MIN && fvco <= FVCO_MAX) {
> > +			pll_clk = fvco / VCU_PLL_DIV2;
> > +			if (fvco % VCU_PLL_DIV2 != 0)
> > +				pll_clk++;
> > +			mod = pll_clk % coreclk;
> > +			if (mod < LIMIT) {
> > +				divisor_core = pll_clk / coreclk;
> > +			} else if (coreclk - mod < LIMIT) {
> > +				divisor_core = pll_clk / coreclk;
> > +				divisor_core++;
> > +			} else {
> > +				continue;
> > +			}
> > +			if (divisor_core >= DIVISOR_MIN &&
> > +			    divisor_core <= DIVISOR_MAX) {
> > +				found = cfg;
> > +				divisor_mcu = pll_clk / mcuclk;
> > +				mod = pll_clk % mcuclk;
> > +				if (mcuclk - mod < LIMIT)
> > +					divisor_mcu++;
> > +				break;
This is the break statement to exit when proper value is find.
> > +			}
> > +		}
> > +	}
> > +
> > +	if (!found) {
> > +		dev_err(xvcu->dev, "Invalid clock combination.\n");
> > +		return -EINVAL;
> > +	}
> 
> [snip]
> 
> --
> ~Randy