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Subject: Re: [RFC] fpga: dfl: a prototype uio driver
To:     Greg KH <gregkh@linuxfoundation.org>
Cc:     yilun.xu@intel.com, hao.wu@intel.com, mdf@kernel.org,
        linux-kernel@vger.kernel.org, linux-fpga@vger.kernel.org
References: <20201206215554.350230-1-trix@redhat.com>
 <X83hkdgrMysGuUdL@kroah.com>
From:   Tom Rix <trix@redhat.com>
Message-ID: <53097eaf-02ee-8e41-9738-107115dc9dcd@redhat.com>
Date:   Mon, 7 Dec 2020 05:07:05 -0800
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On 12/7/20 12:02 AM, Greg KH wrote:
> On Sun, Dec 06, 2020 at 01:55:54PM -0800, trix@redhat.com wrote:
>> From: Tom Rix <trix@redhat.com>
>>
>> >From [PATCH 0/2] UIO support for dfl devices
>> https://lore.kernel.org/linux-fpga/1602828151-24784-1-git-send-email-yilun.xu@intel.com/
> Why is this here?

As reference, Yilun's work has precedence for a uio driver and this rfc is trying to address what i believe is a sticking point of the driver override.  This rfc is some code i hacked out to show the idea and move uio support along.  I would like to see uio support for at least the unclaimed feature id's because this would make it easier for them to be developed.

>> Here is an idea to have uio support with no driver override.
>>
>> This makes UIO the primary driver interface because every feature
>> will have one and makes the existing platform driver interface
>> secondary.  There will be a new burden for locking write access when
>> they compete.
>>
>> Example shows finding the fpga's temperture.
>>
>> Signed-off-by: Tom Rix <trix@redhat.com>
>> ---
>>  drivers/fpga/dfl-fme-main.c |  9 +++-
>>  drivers/fpga/dfl-uio.c      | 96 +++++++++++++++++++++++++++++++++++++
>>  drivers/fpga/dfl.c          | 44 ++++++++++++++++-
>>  drivers/fpga/dfl.h          |  9 ++++
>>  uio.c                       | 56 ++++++++++++++++++++++
>>  5 files changed, 212 insertions(+), 2 deletions(-)
>>  create mode 100644 drivers/fpga/dfl-uio.c
>>  create mode 100644 uio.c
>>
>> diff --git a/drivers/fpga/dfl-fme-main.c b/drivers/fpga/dfl-fme-main.c
>> index 037dc4f946f0..3323e90a18c4 100644
>> --- a/drivers/fpga/dfl-fme-main.c
>> +++ b/drivers/fpga/dfl-fme-main.c
>> @@ -709,12 +709,18 @@ static int fme_probe(struct platform_device *pdev)
>>  	if (ret)
>>  		goto dev_destroy;
>>  
>> -	ret = dfl_fpga_dev_ops_register(pdev, &fme_fops, THIS_MODULE);
>> +	ret = dfl_fpga_dev_feature_init_uio(pdev, DFH_TYPE_FIU);
>>  	if (ret)
>>  		goto feature_uinit;
>>  
>> +	ret = dfl_fpga_dev_ops_register(pdev, &fme_fops, THIS_MODULE);
>> +	if (ret)
>> +		goto feature_uinit_uio;
>> +
>>  	return 0;
>>  
>> +feature_uinit_uio:
>> +	dfl_fpga_dev_feature_uinit_uio(pdev, DFH_TYPE_FIU);
>>  feature_uinit:
>>  	dfl_fpga_dev_feature_uinit(pdev);
>>  dev_destroy:
>> @@ -726,6 +732,7 @@ exit:
>>  static int fme_remove(struct platform_device *pdev)
>>  {
>>  	dfl_fpga_dev_ops_unregister(pdev);
>> +	dfl_fpga_dev_feature_uinit_uio(pdev, DFH_TYPE_FIU);
>>  	dfl_fpga_dev_feature_uinit(pdev);
>>  	fme_dev_destroy(pdev);
>>  
>> diff --git a/drivers/fpga/dfl-uio.c b/drivers/fpga/dfl-uio.c
>> new file mode 100644
>> index 000000000000..7610ee0b19dc
>> --- /dev/null
>> +++ b/drivers/fpga/dfl-uio.c
>> @@ -0,0 +1,96 @@
>> +/* SPDX-License-Identifier: GPL-2.0 */
>> +/*
>> + * prototype dfl uio driver
>> + *
>> + * Copyright Tom Rix 2020
>> + */
>> +#include <linux/module.h>
>> +#include "dfl.h"
>> +
>> +static irqreturn_t dfl_uio_handler(int irq, struct uio_info *info)
>> +{
>> +	return IRQ_HANDLED;
>> +}
>> +
>> +static int dfl_uio_mmap(struct uio_info *info, struct vm_area_struct *vma)
>> +{
>> +	int ret = -ENODEV;
>> +	return ret;
> Did you run this through checkpatch?
>
> Does the code make sense?
>
>> +}
>> +
>> +static int dfl_uio_open(struct uio_info *info, struct inode *inode)
>> +{
>> +	int ret = -ENODEV;
>> +	struct dfl_feature *feature = container_of(info, struct dfl_feature, uio);
>> +	if (feature->dev)
>> +		mutex_lock(&feature->lock);
>> +
>> +	ret = 0;
>> +	return ret;
> Same here, does this make sense?
>
> And wait, you are having userspace grab a kernel lock?  What could go
> wrong?  :(
>
Yes, this is the bad part of this idea.

Tom


>> +}
>> +
>> +static int dfl_uio_release(struct uio_info *info, struct inode *inode)
>> +{
>> +	int ret = -ENODEV;
>> +	struct dfl_feature *feature = container_of(info, struct dfl_feature, uio);
>> +	if (feature->dev)
>> +		mutex_unlock(&feature->lock);
>> +
>> +	ret = 0;
>> +	return ret;
>> +}
>> +
>> +static int dfl_uio_irqcontrol(struct uio_info *info, s32 irq_on)
>> +{
>> +	int ret = -ENODEV;
>> +	return ret;
>> +}
>> +
>> +int dfl_uio_add(struct dfl_feature *feature)
>> +{
>> +	struct uio_info *uio = &feature->uio;
>> +	struct resource *res =
>> +		&feature->dev->resource[feature->resource_index];
>> +	int ret = 0;
>> +
>> +	uio->name = kasprintf(GFP_KERNEL, "dfl-uio-%llx", feature->id);
>> +	if (!uio->name) {
>> +		ret = -ENOMEM;
>> +		goto exit;
>> +	}
>> +
>> +	uio->version = "0.1";
>> +	uio->mem[0].memtype = UIO_MEM_PHYS;
>> +	uio->mem[0].addr = res->start & PAGE_MASK;
>> +	uio->mem[0].offs = res->start & ~PAGE_MASK;
>> +	uio->mem[0].size = (uio->mem[0].offs + resource_size(res)
>> +			    + PAGE_SIZE - 1) & PAGE_MASK;
>> +	/* How are nr_irqs > 1 handled ??? */
>> +	if (feature->nr_irqs == 1)
>> +		uio->irq = feature->irq_ctx[0].irq;
>> +	uio->handler = dfl_uio_handler;
>> +	//uio->mmap = dfl_uio_mmap;
> ???
>
> I don't understand what this patch is trying to show...
> thanks,
>
> greg k-h
>