Re: [PATCH v4 2/5] remoteproc: qcom: Introduce driver to store pil info in IMEM

[Bjorn Andersson <bjorn.andersson@linaro.org>]

On Tue 10 Mar 13:29 PDT 2020, Stephen Boyd wrote:

> Quoting Bjorn Andersson (2020-03-09 23:33:35)
> > A region in IMEM is used to communicate load addresses of remoteproc to
> > post mortem debug tools. Implement a driver that can be used to store
> > this information in order to enable these tools to process collected
> > ramdumps.
> > 
> > Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
> > ---
> > 
> > Changes since v3:
> > - Don't carry shadow of all entries
> > - Reworked indexing of entries in qcom_pil_info_store()
> > - Marked global __read_mostly
> > 
> > Stephen requested, in v3, that the driver should be turned into a library that,
> > in the context of the remoteproc drivers, would resolve the pil info region and
> > update an appropriate entry, preferably a statically assigned one.
> > 
> > Unfortunately the entries must be packed, so it's not possible to pre-assign
> > entries for each remoteproc, in case some of them aren't booted. Further more,
> > it turns out that the IMEM region must be zero-initialized in order to have a
> > reliable way to determining which entries are available.
> > 
> > We therefor have the need for global mutual exclusion and a mechanism that is
> > guaranteed to run before any clients attempt to update the content - so the
> > previously proposed design is maintained.
> 
> The library could have a static variable that tracks when it's been
> called once, holds a lock to protect concurrent access and then zero
> initializes on the first call. 
> 

For the benefit of not having the is_available call then? I presume we
still want the compatible on the node, so the core will still allocate a
struct platform_device for us...

(I'm okay with reworking it that way)

> > diff --git a/drivers/remoteproc/qcom_pil_info.c b/drivers/remoteproc/qcom_pil_info.c
> > new file mode 100644
> > index 000000000000..0ddfb2639b7f
> > --- /dev/null
> > +++ b/drivers/remoteproc/qcom_pil_info.c
> > @@ -0,0 +1,180 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +/*
> > + * Copyright (c) 2019-2020 Linaro Ltd.
> > + */
> > +#include <linux/kernel.h>
> > +#include <linux/mfd/syscon.h>
> > +#include <linux/module.h>
> > +#include <linux/mutex.h>
> > +#include <linux/of.h>
> > +#include <linux/of_address.h>
> > +#include <linux/platform_device.h>
> > +#include <linux/regmap.h>
> > +#include <linux/slab.h>
> > +
> > +#define PIL_RELOC_NAME_LEN     8
> > +
> > +struct pil_reloc_entry {
> > +       char name[PIL_RELOC_NAME_LEN];
> > +       __le64 base;
> > +       __le32 size;
> 
> Why are these little endian? Isn't regmap doing endian swaps?
> 

Ugh, you're right. The regmap is created with "default" endian and
32-bit word size by syscon. So presumably this won't work and I must
have missed it when I dumped imem to check the end result.

> > +} __packed;
> 
> Is __packed necessary? It looks like things are naturally aligned
> already.
> 

No, it should be fine.

> > +
> > +struct pil_reloc {
> > +       struct device *dev;
> > +       struct regmap *map;
> > +       size_t offset;
> > +       size_t num_entries;
> > +       size_t entry_size;
> > +};
> > +
> > +static struct pil_reloc *_reloc __read_mostly;
> > +static DEFINE_MUTEX(reloc_mutex);
> > +
> > +/**
> > + * qcom_pil_info_store() - store PIL information of image in IMEM
> > + * @image:     name of the image
> > + * @base:      base address of the loaded image
> > + * @size:      size of the loaded image
> > + *
> > + * Return: 0 on success, negative errno on failure
> > + */
> > +int qcom_pil_info_store(const char *image, phys_addr_t base, size_t size)
> > +{
> > +       struct pil_reloc_entry entry;
> > +       unsigned int offset;
> > +       int selected = -1;
> > +       int ret;
> > +       int i;
> > +
> > +       offset = _reloc->offset;
> > +
> > +       mutex_lock(&reloc_mutex);
> > +       for (i = 0; i < _reloc->num_entries; i++) {
> > +               ret = regmap_bulk_read(_reloc->map, offset, &entry, _reloc->entry_size);
> > +               if (ret < 0)
> > +                       continue;
> > +
> > +               if (!entry.name[0]) {
> > +                       if (selected == -1)
> > +                               selected = offset;
> > +                       continue;
> 
> Why not goto found?
> 

Didn't think hard enough about it, but you're right - per the need for
packing of entries, if we hit a !name[0] that means there won't be any
matches further down the list.

> > +               }
> > +
> > +               if (!strncmp(entry.name, image, sizeof(entry.name))) {
> > +                       selected = offset;
> > +                       goto found;
> 
> Why not goto found_again? And then jump over the strscpy() in this case?
> 

+1

> > +               }
> > +
> > +               offset += sizeof(entry);
> > +       }
> > +
> > +       if (selected == -1) {
> 
> Do we need this check? It should have been jumped over if it found it?
> 

Per above reasoning this can now go.

> > +               dev_warn(_reloc->dev, "insufficient PIL info slots\n");
> > +               ret = -ENOMEM;
> > +               goto unlock;
> > +       }
> > +
> > +found:
> > +       strscpy(entry.name, image, ARRAY_SIZE(entry.name));
> > +       entry.base = base;
> > +       entry.size = size;
> 
> Sparse should complain here.
> 

You're right.

> > +
> > +       ret = regmap_bulk_write(_reloc->map, selected, &entry, _reloc->entry_size);
> 
> It would make a lot more sense to me if this was written with plain
> readl/writel logic. Then I don't have to think about structs being
> stored in I/O memory regions, and instead I can concentrate on there
> being two 64-bit registers for name and base and one 32-bit register for
> the size.
> 

Seems like this has to change, based on the per-"register" endian
handling in the regmap.

> > +unlock:
> > +       mutex_unlock(&reloc_mutex);
> > +
> > +       return ret;
> > +}
> > +EXPORT_SYMBOL_GPL(qcom_pil_info_store);
> > +
> > +/**
> > + * qcom_pil_info_available() - query if the pil info is probed
> > + *
> > + * Return: boolean indicating if the pil info device is probed
> > + */
> > +bool qcom_pil_info_available(void)
> > +{
> > +       return !!_reloc;
> > +}
> > +EXPORT_SYMBOL_GPL(qcom_pil_info_available);
> > +
> > +static int pil_reloc_probe(struct platform_device *pdev)
> > +{
> > +       struct pil_reloc_entry entry = {0};
> > +       struct pil_reloc *reloc;
> > +       struct resource *res;
> > +       struct resource imem;
> > +       unsigned int offset;
> > +       int ret;
> > +       int i;
> > +
> > +       reloc = devm_kzalloc(&pdev->dev, sizeof(*reloc), GFP_KERNEL);
> > +       if (!reloc)
> > +               return -ENOMEM;
> > +
> > +       reloc->dev = &pdev->dev;
> > +
> > +       res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> > +       if (!res)
> > +               return -EINVAL;
> > +
> > +       /* reloc->offset is relative to parent (IMEM) base address */
> > +       ret = of_address_to_resource(pdev->dev.of_node->parent, 0, &imem);
> > +       if (ret < 0)
> > +               return ret;
> > +
> > +       reloc->offset = res->start - imem.start;
> > +       reloc->num_entries = resource_size(res) / sizeof(entry);
> > +
> > +       reloc->map = syscon_node_to_regmap(pdev->dev.parent->of_node);
> > +       if (IS_ERR(reloc->map))
> > +               return PTR_ERR(reloc->map);
> > +
> > +       ret = regmap_get_val_bytes(reloc->map);
> > +       if (ret < 0)
> > +               return -EINVAL;
> > +       reloc->entry_size = sizeof(entry) / ret;
> > +
> > +       offset = reloc->offset;
> > +       for (i = 0; i < reloc->num_entries; i++, offset += sizeof(entry)) {
> > +               ret = regmap_bulk_write(reloc->map, offset, &entry,
> > +                                       reloc->entry_size);
> > +               if (ret < 0)
> > +                       return ret;
> > +       }
> 
> This would be a lot easier to read with a memset_io().
> 

Yes, indeed.

> > +
> > +       mutex_lock(&reloc_mutex);
> > +       _reloc = reloc;
> > +       mutex_unlock(&reloc_mutex);
> > +
> > +       return 0;
> > +}
> > +
> > +static int pil_reloc_remove(struct platform_device *pdev)
> > +{
> > +       mutex_lock(&reloc_mutex);
> > +       _reloc = NULL;
> > +       mutex_unlock(&reloc_mutex);
> > +
> > +       return 0;
> > +}
> > +
> > +static const struct of_device_id pil_reloc_of_match[] = {
> > +       { .compatible = "qcom,pil-reloc-info" },
> > +       {}
> > +};
> > +MODULE_DEVICE_TABLE(of, pil_reloc_of_match);
> > +
> > +static struct platform_driver pil_reloc_driver = {
> 
> I still don't understand the need for a platform device driver and probe
> ordering. It's not a device in the usual ways, it's just some memory
> that's lying around and always there!

I agree, but the device will be created regardless of us attaching to it
or not - following the fact that it's used to deal with reboot reasons
on some platforms.

> Why can't we search in DT for the
> imem node and then find the pil reloc info compatible string on the
> first call to this library? Then we don't need an API to see if the
> device has probed yet (qcom_pil_info_available)

I think this sounds reasonable.

> and we can just ioremap
> some region of memory that's carved out for this reason. Forcing
> everything through the regmap is mostly adding pain.
> 

My concern here was simply that we'll end up ioremapping various small
chunks of the imem region 10 (or so) times. But I agree that things
would be cleaner here.

Regards,
Bjorn

> > +       .probe = pil_reloc_probe,