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Re: [PATCH v16 6/6] ARM: socfpga: fpga bridge driver support

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  Re: [PATCH v16 6/6] ARM: socfpga: fpga bridge driver support Andrea Galbusera <gizero@gmail.com> - 2016-07-28 12:30 +0200
    Re: [PATCH v16 6/6] ARM: socfpga: fpga bridge driver support Trent Piepho <tpiepho@kymetacorp.com> - 2016-07-28 22:40 +0200

#1451867 — Re: [PATCH v16 6/6] ARM: socfpga: fpga bridge driver support

On Fri, Jun 10, 2016 at 4:18 AM, Trent Piepho <tpiepho@kymetacorp.com> wrote:
> On Fri, 2016-02-05 at 15:30 -0600, atull@opensource.altera.com wrote:
>> Supports Altera SOCFPGA bridges:
>>  * fpga2sdram
>>  * fpga2hps
>>  * hps2fpga
>>  * lwhps2fpga
>>
>> Allows enabling/disabling the bridges through the FPGA
>> Bridge Framework API functions.
>
> I'm replying to v16 because it exists on gmane, while v17 appears not
> to.  lkml.org's forward feature appears to be broken so I can't reply to
> that message (no way to get message-id).  But v17 of this patch should
> be the same.  If a v18 was posted, I've not been able to find it.
>
>> diff --git a/drivers/fpga/altera-hps2fpga.c b/drivers/fpga/altera-hps2fpga.c
>> new file mode 100644
>> index 0000000..c15df47
>> --- /dev/null
>> +++ b/drivers/fpga/altera-hps2fpga.c
>> @@ -0,0 +1,213 @@
>> +/*
>> + * FPGA to/from HPS Bridge Driver for Altera SoCFPGA Devices
>> + *
>> + *  Copyright (C) 2013-2015 Altera Corporation, All Rights Reserved.
>> + *
>> + * This program is free software; you can redistribute it and/or modify it
>> + * under the terms and conditions of the GNU General Public License,
>> + * version 2, as published by the Free Software Foundation.
>> + *
>> + * This program is distributed in the hope it will be useful, but WITHOUT
>> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
>> + * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
>> + * more details.
>> + *
>> + * You should have received a copy of the GNU General Public License along with
>> + * this program.  If not, see <http://www.gnu.org/licenses/>.
>> + */
>> +
>> +/*
>> + * This driver manages bridges on a Altera SOCFPGA between the ARM host
>> + * processor system (HPS) and the embedded FPGA.
>> + *
>> + * This driver supports enabling and disabling of the configured ports, which
>> + * allows for safe reprogramming of the FPGA, assuming that the new FPGA image
>> + * uses the same port configuration.  Bridges must be disabled before
>> + * reprogramming the FPGA and re-enabled after the FPGA has been programmed.
>> + */
>> +
>> +#include <linux/clk.h>
>> +#include <linux/fpga/fpga-bridge.h>
>> +#include <linux/kernel.h>
>> +#include <linux/mfd/syscon.h>
>> +#include <linux/module.h>
>> +#include <linux/of_platform.h>
>> +#include <linux/regmap.h>
>> +#include <linux/reset.h>
>> +
>> +#define ALT_L3_REMAP_OFST                    0x0
>> +#define ALT_L3_REMAP_MPUZERO_MSK             0x00000001
>> +#define ALT_L3_REMAP_H2F_MSK                 0x00000008
>> +#define ALT_L3_REMAP_LWH2F_MSK                       0x00000010
>> +
>> +#define HPS2FPGA_BRIDGE_NAME                 "hps2fpga"
>> +#define LWHPS2FPGA_BRIDGE_NAME                       "lwhps2fpga"
>> +#define FPGA2HPS_BRIDGE_NAME                 "fpga2hps"
>> +
>> +struct altera_hps2fpga_data {
>> +     const char *name;
>> +     struct reset_control *bridge_reset;
>> +     struct regmap *l3reg;
>> +     /* The L3 REMAP register is write only, so keep a cached value. */
>> +     unsigned int l3_remap_value;
>> +     unsigned int remap_mask;
>> +     struct clk *clk;
>> +};
>> +
>> +static int alt_hps2fpga_enable_show(struct fpga_bridge *bridge)
>> +{
>> +     struct altera_hps2fpga_data *priv = bridge->priv;
>> +
>> +     return reset_control_status(priv->bridge_reset);
>> +}
>> +
>> +static int _alt_hps2fpga_enable_set(struct altera_hps2fpga_data *priv,
>> +                                 bool enable)
>> +{
>> +     int ret;
>> +
>> +     /* bring bridge out of reset */
>> +     if (enable)
>> +             ret = reset_control_deassert(priv->bridge_reset);
>> +     else
>> +             ret = reset_control_assert(priv->bridge_reset);
>> +     if (ret)
>> +             return ret;
>> +
>> +     /* Allow bridge to be visible to L3 masters or not */
>> +     if (priv->remap_mask) {
>> +             priv->l3_remap_value |= ALT_L3_REMAP_MPUZERO_MSK;
>
> Doesn't seem like this belongs here.  I realize the write-only register
> is a problem.  Maybe the syscon driver should be initializing this
> value?
>
>> +
>> +             if (enable)
>> +                     priv->l3_remap_value |= priv->remap_mask;
>> +             else
>> +                     priv->l3_remap_value &= ~priv->remap_mask;
>> +
>> +             ret = regmap_write(priv->l3reg, ALT_L3_REMAP_OFST,
>> +                                priv->l3_remap_value);
>
> This isn't going work if more than one bridge is used.  Each bridge has
> its own priv and thus priv->l3_remap_value.  Each bridge's priv will
> have just the bit for it's own remap set.  The 2nd bridge to be enabled
> will turn off the 1st bridge when it re-write the l3 register.

I can confirm this is exactly what happens with tag
"rel_socfpga-4.1.22-ltsi_16.06.02_pr" of socfpga-4.1.22-ltsi branch
from altera-opensource/linux-socfpga which includes more or less the
code in this patch. If you have 2 bridges (lw-hps2fpga and hps2fpga)
you end up with only one of them being visible. Easily spot by logging
l3_remap_value being passed to regmap_write()...

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#1452097

On Thu, 2016-07-28 at 10:21 -0500, atull wrote:
> > >
> > > This isn't going work if more than one bridge is used.  Each bridge has
> > > its own priv and thus priv->l3_remap_value.  Each bridge's priv will
> > > have just the bit for it's own remap set.  The 2nd bridge to be enabled
> > > will turn off the 1st bridge when it re-write the l3 register.
> > 
> > I can confirm this is exactly what happens with tag
> > "rel_socfpga-4.1.22-ltsi_16.06.02_pr" of socfpga-4.1.22-ltsi branch
> > from altera-opensource/linux-socfpga which includes more or less the
> > code in this patch. If you have 2 bridges (lw-hps2fpga and hps2fpga)
> > you end up with only one of them being visible. Easily spot by logging
> > l3_remap_value being passed to regmap_write()...
> > 
> 
> Anatolij kindly provided a patch for this issue.  I'll push it
> to my github repo when I can.

I still think a better solution would be to allow the syscon driver
manage shared access.  The purpose of syscon is to manage access to a
shared resource from multiple devices.  And regmap already has the
ability to cache a write-only register and allow thread safe access to
modify bits in said register.  The problem is just the pain of trying to
do anything to syscon DT bindings.  Something like "write-only" in the
syscon binding that sets a couple values in the regmap_config is all
that's necessary.

Might as well not use syscon at all and have the bridge driver map the
l3regs itself, since it doesn't really use syscon for anything.

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