From: Mark Rutland <mark.rutland@arm.com>
To: Xiubo Li <Li.Xiubo@freescale.com>
Cc: "linux-pwm@vger.kernel.org" <linux-pwm@vger.kernel.org>,
"linux@arm.linux.org.uk" <linux@arm.linux.org.uk>,
"ian.campbell@citrix.com" <ian.campbell@citrix.com>,
Pawel Moll <Pawel.Moll@arm.com>,
"swarren@wwwdotorg.org" <swarren@wwwdotorg.org>,
"s.hauer@pengutronix.de" <s.hauer@pengutronix.de>,
"linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
Alison Wang <b18965@freescale.com>,
"tomasz.figa@gmail.com" <tomasz.figa@gmail.com>,
"rob.herring@calxeda.com" <rob.herring@calxeda.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"r65073@freescale.com" <r65073@freescale.com>,
Jingchang Lu <b35083@freescale.com>,
"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
"thierry.reding@gmail.com" <thierry.reding@gmail.com>,
"rob@landley.net" <rob@landley.net>,
"galak@codeaurora.org" <galak@codeaurora.org>,
"grant.likely@linaro.org" <grant.likely@linar>
Subject: Re: [RFC] pwm: Add Freescale FTM PWM driver support
Date: Mon, 2 Dec 2013 12:34:06 +0000 [thread overview]
Message-ID: <20131202123406.GK12952@e106331-lin.cambridge.arm.com> (raw)
In-Reply-To: <1385979309-10505-1-git-send-email-Li.Xiubo@freescale.com>
On Mon, Dec 02, 2013 at 10:15:09AM +0000, Xiubo Li wrote:
> The FTM PWM device can be found on Vybrid VF610 Tower and
> Layerscape LS-1 SoCs.
>
> Signed-off-by: Xiubo Li <Li.Xiubo@freescale.com>
> Signed-off-by: Alison Wang <b18965@freescale.com>
> Signed-off-by: Jingchang Lu <b35083@freescale.com>
> ---
>
> I'm sending the RFC patch about the FTM IP block registers read and write
> endian fix for comments and more parcticed ideas.
>
> In Vybird VF610 Tower, all the IP blocks expect LE data. In the LS-1, some of
> the IP blocks expect LE data, while others expect BE data. And the CPU always
> operates in LE mode in these two platforms.
Could you elaborate on "expect BE data" please? Is this all registers
within a given device, or a subset thereof? Are there data structrues
involved (i.e. buffers)?
>
> So now I must take care of all these two cases. I'm not very sure if there is
> other better ways to resolve this problem. In this patch I have implemented
> two functions fsl_pwm_readl() and fsl_pwm_writel() to replace readl() and
> writel(). At the same time there should add one "endianess" property in the DT
> file.
If you're adding DT properties, binding updates are helpful to describe
their intended use.
[...]
> +static inline u32 fsl_pwm_readl(struct fsl_pwm_chip *fpc, void __iomem *reg)
> +{
> + u32 val;
> +
> + val = __raw_readl(reg);
> +
> + if (fpc->endianess == FTM_BIG)
> + return be32_to_cpu(val);
> + else
> + return le32_to_cpu(val);
> +}
> +
> +static inline void fsl_pwm_writel(struct fsl_pwm_chip *fpc, u32 val,
> + void __iomem *reg)
> +{
> + if (fpc->endianess == FTM_BIG)
> + val = cpu_to_be32(val);
> + else
> + val = cpu_to_le32(val);
> +
> + __raw_writel(val, reg);
> +}
Using the __raw variants also loses you the memory barriers. Does this
create any ordering issues in the rest of the driver?
[...]
> +static int fsl_pwm_probe(struct platform_device *pdev)
> +{
> + int ret;
> + const char *endianess;
> + struct fsl_pwm_chip *fpc;
> + struct resource *res;
> + struct device_node *np = pdev->dev.of_node;
> +
> + fpc = devm_kzalloc(&pdev->dev, sizeof(*fpc), GFP_KERNEL);
> + if (!fpc)
> + return -ENOMEM;
> +
> + mutex_init(&fpc->lock);
> +
> + fpc->chip.dev = &pdev->dev;
> +
> + ret = fsl_pwm_parse_clk_ps(fpc);
> + if (ret < 0)
> + return ret;
> +
> + if (of_property_read_string(np, "endianess", &endianess))
> + pr_warning("missing \"endianess\" property, "
> + "the FTM IP block is little "
> + "endian as default\n");
> + else if (!strcmp("big", endianess))
> + fpc->endianess = FTM_BIG;
Please don't do this.
One option is to have a new compatible string -- a big-endian device
can't be poked in the same way as its little-endian variants, so they're
not compatible. You can then associate some data with the compatible
strings to figure out which accessors to use.
If you really want this to be a separate property, make it a boolean
property (e.g. "fsl,big-endian", which you can read with
of_property_read_bool. There's no need for this to be a string.
I'd prefer the compatible string option.
Thanks,
Mark.
next prev parent reply other threads:[~2013-12-02 12:34 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-02 10:15 [RFC] pwm: Add Freescale FTM PWM driver support Xiubo Li
2013-12-02 12:34 ` Mark Rutland [this message]
2013-12-03 4:02 ` Li Xiubo
2013-12-03 10:36 ` Mark Rutland
2013-12-04 3:12 ` Li Xiubo
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