RE: [EXT] Re: [PATCH v3 4/4] soc: imx8m: change to use platform driver

[Alice Guo]

> -----Original Message-----
> From: Krzysztof Kozlowski <krzk@xxxxxxxxxx>
> Sent: 2020年11月15日 0:41
> To: Alice Guo <alice.guo@xxxxxxx>
> Cc: robh+dt@xxxxxxxxxx; shawnguo@xxxxxxxxxx; s.hauer@xxxxxxxxxxxxxx;
> dl-linux-imx <linux-imx@xxxxxxx>; Peng Fan <peng.fan@xxxxxxx>;
> devicetree@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> Subject: [EXT] Re: [PATCH v3 4/4] soc: imx8m: change to use platform driver
> 
> Caution: EXT Email
> 
> On Fri, Nov 13, 2020 at 07:04:09PM +0800, Alice Guo wrote:
> > Directly reading ocotp register depends on that bootloader enables
> > ocotp clk, which is not always effective, so change to use nvmem API.
> > Using nvmem API requires to support driver defer probe and thus change
> > soc-imx8m.c to use platform driver.
> >
> > The other reason is that directly reading ocotp register causes kexec
> > kernel hang because the 1st kernel running will disable unused clks
> > after kernel boots up, and then ocotp clk will be disabled even if
> > bootloader enables it. When kexec kernel, ocotp clk needs to be
> > enabled before reading ocotp registers, and nvmem API with platform
> > driver supported can accomplish this.
> >
> > Old .dts files can also work.
> >
> > Signed-off-by: Alice Guo <alice.guo@xxxxxxx>
> > ---
> >  drivers/soc/imx/soc-imx8m.c | 89
> > ++++++++++++++++++++++++++++++++-----
> >  1 file changed, 79 insertions(+), 10 deletions(-)
> >
> > diff --git a/drivers/soc/imx/soc-imx8m.c b/drivers/soc/imx/soc-imx8m.c
> > index cc57a384d74d..af2c0dbe8291 100644
> > --- a/drivers/soc/imx/soc-imx8m.c
> > +++ b/drivers/soc/imx/soc-imx8m.c
> > @@ -5,6 +5,8 @@
> >
> >  #include <linux/init.h>
> >  #include <linux/io.h>
> > +#include <linux/module.h>
> > +#include <linux/nvmem-consumer.h>
> >  #include <linux/of_address.h>
> >  #include <linux/slab.h>
> >  #include <linux/sys_soc.h>
> > @@ -29,7 +31,7 @@
> >
> >  struct imx8_soc_data {
> >       char *name;
> > -     u32 (*soc_revision)(void);
> > +     u32 (*soc_revision)(struct device *dev, int flag);
> >  };
> >
> >  static u64 soc_uid;
> > @@ -50,7 +52,7 @@ static u32 imx8mq_soc_revision_from_atf(void)
> >  static inline u32 imx8mq_soc_revision_from_atf(void) { return 0; };
> > #endif
> >
> > -static u32 __init imx8mq_soc_revision(void)
> > +static u32 __init imx8mq_soc_revision(struct device *dev, int flag)
> >  {
> >       struct device_node *np;
> >       void __iomem *ocotp_base;
> > @@ -75,9 +77,17 @@ static u32 __init imx8mq_soc_revision(void)
> >                       rev = REV_B1;
> >       }
> >
> > -     soc_uid = readl_relaxed(ocotp_base + OCOTP_UID_HIGH);
> > -     soc_uid <<= 32;
> > -     soc_uid |= readl_relaxed(ocotp_base + OCOTP_UID_LOW);
> > +     if (flag) {
> > +             int ret = 0;
> > +
> > +             ret = nvmem_cell_read_u64(dev, "soc_unique_id",
> &soc_uid);
> > +             if (ret)
> > +                     return ret;
> > +     } else {
> > +             soc_uid = readl_relaxed(ocotp_base + OCOTP_UID_HIGH);
> > +             soc_uid <<= 32;
> > +             soc_uid |= readl_relaxed(ocotp_base + OCOTP_UID_LOW);
> > +     }
> >
> >       iounmap(ocotp_base);
> >       of_node_put(np);
> > @@ -107,7 +117,7 @@ static void __init imx8mm_soc_uid(void)
> >       of_node_put(np);
> >  }
> >
> > -static u32 __init imx8mm_soc_revision(void)
> > +static u32 __init imx8mm_soc_revision(struct device *dev, int flag)
> >  {
> >       struct device_node *np;
> >       void __iomem *anatop_base;
> > @@ -125,7 +135,15 @@ static u32 __init imx8mm_soc_revision(void)
> >       iounmap(anatop_base);
> >       of_node_put(np);
> >
> > -     imx8mm_soc_uid();
> > +     if (flag) {
> > +             int ret = 0;
> > +
> > +             ret = nvmem_cell_read_u64(dev, "soc_unique_id",
> &soc_uid);
> > +             if (ret)
> > +                     return ret;
> > +     } else {
> > +             imx8mm_soc_uid();
> > +     }
> >
> >       return rev;
> >  }
> > @@ -158,12 +176,21 @@ static __maybe_unused const struct of_device_id
> imx8_soc_match[] = {
> >       { }
> >  };
> >
> > +static __maybe_unused const struct of_device_id imx8m_soc_match[] = {
> 
> Could this really be unused?

[Alice Guo] I will delete "__maybe_unused".

> 
> > +     { .compatible = "fsl,imx8mq-soc", .data = &imx8mq_soc_data, },
> > +     { .compatible = "fsl,imx8mm-soc", .data = &imx8mm_soc_data, },
> > +     { .compatible = "fsl,imx8mn-soc", .data = &imx8mn_soc_data, },
> > +     { .compatible = "fsl,imx8mp-soc", .data = &imx8mp_soc_data, },
> > +     { }
> > +};
> > +MODULE_DEVICE_TABLE(of, imx8m_soc_match);
> 
> You already have "imx8_soc_match" which covers imx8m and now you add
> "imx8m_soc_match" which also covers imx8m. Such naming is a pure
> confusion.
> 

[Alice Guo] device_initcall is executed earlier than module_platform_driver. imx8_soc_init will judge
whether there is "fsl,imx8mX-soc" in DTS file. If there is "fsl,imx8mX-soc", it will exit device_initcall and use module_platform_driver. The purpose is to be compatible with the old DTS file which does not have
"fsl,imx8mX-soc".

> > +
> >  #define imx8_revision(soc_rev) \
> >       soc_rev ? \
> >       kasprintf(GFP_KERNEL, "%d.%d", (soc_rev >> 4) & 0xf,  soc_rev &
> 0xf) : \
> >       "unknown"
> >
> > -static int __init imx8_soc_init(void)
> > +static int imx8_soc_init_flag(struct platform_device *pdev, int flag)
> >  {
> >       struct soc_device_attribute *soc_dev_attr;
> >       struct soc_device *soc_dev;
> > @@ -182,7 +209,10 @@ static int __init imx8_soc_init(void)
> >       if (ret)
> >               goto free_soc;
> >
> > -     id = of_match_node(imx8_soc_match, of_root);
> > +     if (flag)
> > +             id = of_match_node(imx8m_soc_match,
> pdev->dev.of_node);
> > +     else
> > +             id = of_match_node(imx8_soc_match, of_root);
> >       if (!id) {
> >               ret = -ENODEV;
> >               goto free_soc;
> > @@ -192,7 +222,13 @@ static int __init imx8_soc_init(void)
> >       if (data) {
> >               soc_dev_attr->soc_id = data->name;
> >               if (data->soc_revision)
> > -                     soc_rev = data->soc_revision();
> > +                     soc_rev = data->soc_revision(&pdev->dev, flag);
> > +
> > +             if (flag) {
> > +                     ret = soc_rev;
> > +                     if (ret < 0)
> > +                             goto free_soc;
> > +             }
> >       }
> >
> >       soc_dev_attr->revision = imx8_revision(soc_rev); @@ -230,4
> > +266,37 @@ static int __init imx8_soc_init(void)
> >       kfree(soc_dev_attr);
> >       return ret;
> >  }
> > +
> > +static int __init imx8_soc_init(void) {
> > +     int ret = 0, flag = 0;
> > +
> > +     if (of_find_compatible_node(NULL, NULL, "fsl,imx8mm-soc") ||
> > +         of_find_compatible_node(NULL, NULL, "fsl,imx8mn-soc") ||
> > +         of_find_compatible_node(NULL, NULL, "fsl,imx8mp-soc") ||
> > +         of_find_compatible_node(NULL, NULL, "fsl,imx8mq-soc"))
> 
> Missing puts.
> 
> Don't duplicate the compatibles, iterate over existing structure... or see
> comments below.  Maybe you could simplify it with something like
> of_find_matching_node_and_match()... but check comments below.

[Alice Guo] I check comments below.

> 
> > +             return 0;
> > +
> > +     ret = imx8_soc_init_flag(NULL, flag);
> > +     return ret;
> > +}
> >  device_initcall(imx8_soc_init);
> 
> Where is the changelog? This was removed previously, now it stays...
> 
> After more thoughs, it looks you have kept it for the purpose of supporting
> existing DTB, but it is not explained. Neither in the source code (which after
> applying this patch looks confusing) nor in commit message.
> 
> In case of old DTB without fsl,imx8mm-soc-like compatibles, it would be better
> to still register a platform driver and create a device
> (of_platform_device_create())). However still this won't solve the problem of
> actually missing device node... so maybe this double entry point is acceptable,
> if properly explained.

[Alice Guo] Sorry, I will add changelog next time. Actually I wrote "Old .dts files can also work." in the commit.

device_initcall is executed earlier than module_platform_driver. imx8_soc_init will judge
whether there is "fsl,imx8mX-soc" in DTS file. If there is "fsl,imx8mX-soc", it will exit device_initcall and use module_platform_driver. Can I keep double entry point?

> 
> > +
> > +static int imx8_soc_init_probe(struct platform_device *pdev) {
> > +     int ret = 0, flag = 1;
> > +
> > +     ret = imx8_soc_init_flag(pdev, flag);
> 
> Never name unspecified booleans like "flag". The same as string variables
> should be named "string", integers should not be named "number".

[Alice Guo] Ok. I will modify it. Can the name of function use suffix "_flag"?

> 
> > +     return ret;
> > +}
> > +
> > +static struct platform_driver imx8_soc_init_driver = {
> > +     .probe = imx8_soc_init_probe,
> > +     .driver = {
> > +             .name = "imx8_soc_init",
> > +             .of_match_table = of_match_ptr(imx8m_soc_match),
> 
> Can it bind without OF? Why it's a of_match_ptr()?
> 

[Alice Guo] I will modify it.

> > +     },
> > +};
> > +
> > +module_platform_driver(imx8_soc_init_driver);
> 
> Here and in all other places (including driver name) this is not a SoC
> initialization (init) driver. You cannot initialize a SoC. This looks like a SoC ID
> driver, so one name could be "imx8_soc_id".
> 

[Alice Guo] I will modify it.

Best regards,
Alice Guo

> Best regards,
> Krzysztof