Date:	Mon, 29 Oct 2012 13:20:56 +0100
From:	Philipp Zabel <p.zabel@...gutronix.de>
To:	Paul Gortmaker <paul.gortmaker@...driver.com>
Cc:	linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <rob.herring@...xeda.com>,
	Shawn Guo <shawn.guo@...aro.org>,
	Richard Zhao <richard.zhao@...escale.com>,
	Huang Shijie <shijie8@...il.com>,
	Dong Aisheng <dong.aisheng@...aro.org>,
	Matt Porter <mporter@...com>, kernel@...gutronix.de,
	devicetree-discuss@...ts.ozlabs.org
Subject: Re: [PATCH v5 2/4] misc: Generic on-chip SRAM allocation driver

Hi Paul,

thank you for your comments.

Am Freitag, den 26.10.2012, 12:07 -0400 schrieb Paul Gortmaker:
> On Thu, Oct 18, 2012 at 10:27 AM, Philipp Zabel <p.zabel@...gutronix.de> wrote:
> > This driver requests and remaps a memory region as configured in the
> > device tree. It serves memory from this region via the genalloc API.
> >
> > Other drivers can retrieve the genalloc pool from a phandle pointing
> > to this drivers' device node in the device tree.
> >
> > Signed-off-by: Philipp Zabel <p.zabel@...gutronix.de>
> > Reviewed-by: Shawn Guo <shawn.guo@...aro.org>
> > ---
> >  Documentation/devicetree/bindings/misc/sram.txt |   17 ++++
> >  drivers/misc/Kconfig                            |    9 ++
> >  drivers/misc/Makefile                           |    1 +
> >  drivers/misc/sram.c                             |  111 +++++++++++++++++++++++
> >  4 files changed, 138 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/misc/sram.txt
> >  create mode 100644 drivers/misc/sram.c
> >
> > diff --git a/Documentation/devicetree/bindings/misc/sram.txt b/Documentation/devicetree/bindings/misc/sram.txt
> > new file mode 100644
> > index 0000000..b64136c
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/misc/sram.txt
> > @@ -0,0 +1,17 @@
> > +Generic on-chip SRAM
> > +
> > +Simple IO memory regions to be managed by the genalloc API.
> > +
> > +Required properties:
> > +
> > +- compatible : sram
> > +
> > +- reg : SRAM iomem address range
> > +
> > +Example:
> > +
> > +sram: sram@...00000 {
> > +       compatible = "sram";
> > +       reg = <0x5c000000 0x40000>; /* 256 KiB SRAM at address 0x5c000000 */
> > +};
> > +
> > diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
> > index b151b7c..c5bbd00 100644
> > --- a/drivers/misc/Kconfig
> > +++ b/drivers/misc/Kconfig
> > @@ -499,6 +499,15 @@ config USB_SWITCH_FSA9480
> >           stereo and mono audio, video, microphone and UART data to use
> >           a common connector port.
> >
> > +config SRAM
> > +       bool "Generic on-chip SRAM driver"
> 
> If it is bool, then why bother with module.h and all the
> MODULE_AUTHOR and similar stuff?

Yes. This driver was a module before I noticed that I then would have to
keep track in genalloc to avoid module unloading while some SRAM is
allocated. It seemed a bit too invasive.

> > +       depends on HAS_IOMEM
> > +       select GENERIC_ALLOCATOR
> > +       help
> > +         This driver allows to declare a memory region to be managed
> > +         by the genalloc API. It is supposed to be used for small
> > +         on-chip SRAM areas found on many ARM SoCs.
> 
> Probably no need to call out ARM specifically here.  I'm pretty sure
> quite a few of the powerpc parts have SRAM too.

Sure, I'll just s/ARM // then.

> > +
> >  source "drivers/misc/c2port/Kconfig"
> >  source "drivers/misc/eeprom/Kconfig"
> >  source "drivers/misc/cb710/Kconfig"
> > diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
> > index 2129377..d845690 100644
> > --- a/drivers/misc/Makefile
> > +++ b/drivers/misc/Makefile
> > @@ -49,3 +49,4 @@ obj-y                         += carma/
> >  obj-$(CONFIG_USB_SWITCH_FSA9480) += fsa9480.o
> >  obj-$(CONFIG_ALTERA_STAPL)     +=altera-stapl/
> >  obj-$(CONFIG_INTEL_MEI)                += mei/
> > +obj-$(CONFIG_SRAM)             += sram.o
> > diff --git a/drivers/misc/sram.c b/drivers/misc/sram.c
> > new file mode 100644
> > index 0000000..7a363f2
> > --- /dev/null
> > +++ b/drivers/misc/sram.c
> > @@ -0,0 +1,111 @@
> > +/*
> > + * Generic on-chip SRAM allocation driver
> > + *
> > + * Copyright (C) 2012 Philipp Zabel, Pengutronix
> > + *
> > + * This program is free software; you can redistribute it and/or
> > + * modify it under the terms of the GNU General Public License
> > + * as published by the Free Software Foundation; either version 2
> > + * of the License, or (at your option) any later version.
> > + * This program is distributed in the hope that 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, write to the Free Software
> > + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
> > + * MA 02110-1301, USA.
> > + */
> > +
> > +#include <linux/kernel.h>
> > +#include <linux/module.h>
> > +#include <linux/init.h>
> > +#include <linux/io.h>
> > +#include <linux/of.h>
> > +#include <linux/platform_device.h>
> > +#include <linux/spinlock.h>
> > +#include <linux/genalloc.h>
> > +
> > +struct sram_dev {
> > +       struct gen_pool *pool;
> > +};
> 
> Assuming you don't ever intend adding more to the struct, then:

See the clock patch. I'm not sure if further functionality will be
needed on any architecture.

> static struct gen_pool *sram_pool;
> 
> instead?

No, a global variable would mean that only one instance of the SRAM
driver can be used. What about chips that have separate SRAM regions?

> And you'll lose the needless indirections in the
> remaining code below, and the kzalloc too (which you
> currently leak, btw).

Memory allocated by devm_kzalloc should be freed by the devres
framework. If I am missing something, could you please elaborate?

> I'd also delete the "/* sentinel */"
> comment too, since it is self evident. (The disease has
> spread by copying from other drivers I see).

I can do that.

> P.
> --
> 
> > +
> > +static int __devinit sram_probe(struct platform_device *pdev)
> > +{
> > +       void __iomem *virt_base;
> > +       struct sram_dev *sram;
> > +       struct resource *res;
> > +       unsigned long size;
> > +       int ret;
> > +
> > +       res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> > +       if (!res)
> > +               return -EINVAL;
> > +
> > +       size = resource_size(res);
> > +
> > +       virt_base = devm_request_and_ioremap(&pdev->dev, res);
> > +       if (!virt_base)
> > +               return -EADDRNOTAVAIL;
> > +
> > +       sram = devm_kzalloc(&pdev->dev, sizeof(*sram), GFP_KERNEL);
> > +       if (!sram)
> > +               return -ENOMEM;
> > +
> > +       sram->pool = gen_pool_create(PAGE_SHIFT, -1);
> > +       if (!sram->pool)
> > +               return -ENOMEM;
> > +
> > +       ret = gen_pool_add_virt(sram->pool, (unsigned long)virt_base,
> > +                               res->start, size, -1);
> > +       if (ret < 0) {
> > +               gen_pool_destroy(sram->pool);
> > +               return ret;
> > +       }
> > +
> > +       platform_set_drvdata(pdev, sram);
> > +
> > +       dev_dbg(&pdev->dev, "SRAM pool: %ld KiB @ 0x%p\n", size / 1024, virt_base);
> > +
> > +       return 0;
> > +}
> > +
> > +static int __devexit sram_remove(struct platform_device *pdev)
> > +{
> > +       struct sram_dev *sram = platform_get_drvdata(pdev);
> > +
> > +       if (gen_pool_avail(sram->pool) < gen_pool_size(sram->pool))
> > +               dev_dbg(&pdev->dev, "removed while SRAM allocated\n");
> > +
> > +       gen_pool_destroy(sram->pool);
> > +
> > +       return 0;
> > +}
> > +
> > +#ifdef CONFIG_OF
> > +static struct of_device_id sram_dt_ids[] = {
> > +       { .compatible = "sram" },
> > +       { /* sentinel */ }
> > +};
> > +#endif
> > +
> > +static struct platform_driver sram_driver = {
> > +       .driver = {
> > +               .name = "sram",
> > +               .of_match_table = of_match_ptr(sram_dt_ids),
> > +       },
> > +       .probe = sram_probe,
> > +       .remove = __devexit_p(sram_remove),
> > +};
> > +
> > +int __init sram_init(void)
> > +{
> > +       return platform_driver_register(&sram_driver);
> > +}
> > +
> > +postcore_initcall(sram_init);
> > +
> > +MODULE_LICENSE("GPL");
> > +MODULE_AUTHOR("Philipp Zabel, Pengutronix");
> > +MODULE_DESCRIPTION("Generic SRAM allocator driver");
> > --
> > 1.7.10.4
> >
> > --
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regards
Philipp

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