Re: [PATCH v3 2/2] dmaengine: uniphier-mdmac: add UniPhier MIO DMAC driver

[Vinod]

On 12-10-18, 01:27, Masahiro Yamada wrote:
> On Sun, Oct 7, 2018 at 1:23 AM Vinod <vkoul@xxxxxxxxxx> wrote:
> > > > > +static int uniphier_mdmac_probe(struct platform_device *pdev)
> > > > > +{
> > > > > +     struct device *dev = &pdev->dev;
> > > > > +     struct uniphier_mdmac_device *mdev;
> > > > > +     struct dma_device *ddev;
> > > > > +     struct resource *res;
> > > > > +     int nr_chans, ret, i;
> > > > > +
> > > > > +     nr_chans = platform_irq_count(pdev);
> > > > > +     if (nr_chans < 0)
> > > > > +             return nr_chans;
> > > > > +
> > > > > +     ret = dma_set_mask(dev, DMA_BIT_MASK(32));
> > > > > +     if (ret)
> > > > > +             return ret;
> > > > > +
> > > > > +     mdev = devm_kzalloc(dev, struct_size(mdev, channels, nr_chans),
> > > > > +                         GFP_KERNEL);
> > > > > +     if (!mdev)
> > > > > +             return -ENOMEM;
> > > > > +
> > > > > +     res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> > > > > +     mdev->reg_base = devm_ioremap_resource(dev, res);
> > > > > +     if (IS_ERR(mdev->reg_base))
> > > > > +             return PTR_ERR(mdev->reg_base);
> > > > > +
> > > > > +     mdev->clk = devm_clk_get(dev, NULL);
> > > > > +     if (IS_ERR(mdev->clk)) {
> > > > > +             dev_err(dev, "failed to get clock\n");
> > > > > +             return PTR_ERR(mdev->clk);
> > > > > +     }
> > > > > +
> > > > > +     ret = clk_prepare_enable(mdev->clk);
> > > > > +     if (ret)
> > > > > +             return ret;
> > > > > +
> > > > > +     ddev = &mdev->ddev;
> > > > > +     ddev->dev = dev;
> > > > > +     dma_cap_set(DMA_PRIVATE, ddev->cap_mask);
> > > > > +     ddev->src_addr_widths = BIT(DMA_SLAVE_BUSWIDTH_UNDEFINED);
> > > > > +     ddev->dst_addr_widths = BIT(DMA_SLAVE_BUSWIDTH_UNDEFINED);
> > > >
> > > > undefined?
> > >
> > > Precisely, I do not know the *_addr_widths.
> >
> > This is "your" controller, you know the capability!
> 
> No, I do not.
> 
> I wrote this driver, but the hardware-internal is not fully documented
> in the datasheet.
> I can see the functionality only from the software point of view.

Ah that is sad!

> > > As far as I read dmaengine/provider.rst
> > > this represents the data bytes that are read/written at a time.
> > >
> > > Really I do not know (care about) the transfer width.
> > >
> > > As I commented in v2, the connection of the device side is hard-wired.
> > > The transfer width cannot be observed from SW view.
> > >
> > > What should I do?
> >
> > Add the widths that are supported by the controller
> 
> To my best knowledge, this DMA engine is connected to a 32-bit bus.
> So, 4 bytes are read/written at a time.
> 
> This HW allows to set the transfer size by byte granularity.
> So, it would be possible to access the data bus
> by 1-byte, 2-bytes, 3-bytes as well.
> 
> I will set the OR of 1, 2, 3, 4 bytes.

that would be better. Also if you can test and verify these and add the
ones you have verified would be even better

> > > > > +static int uniphier_mdmac_remove(struct platform_device *pdev)
> > > > > +{
> > > > > +     struct uniphier_mdmac_device *mdev = platform_get_drvdata(pdev);
> > > > > +
> > > > > +     of_dma_controller_free(pdev->dev.of_node);
> > > > > +     dma_async_device_unregister(&mdev->ddev);
> > > > > +     clk_disable_unprepare(mdev->clk);
> > > >
> > > > at this point your irq is registered and can be fired, the tasklets are
> > > > not killed :(
> > >
> > >
> > > Please let me clarify the concerns here.
> > >
> > > Before the .remove hook is called, all the consumers should
> > > have already put the dma channels.
> > > So, no new descriptor is coming in.
> > >
> > > However,
> > >
> > > Some already-issued descriptors might be remaining, and being processed.
> > >
> > > [1] This DMA engine might be still running
> > >     when clk_disable_unprepare() is being called.
> > >     The register access with its clock disabled
> > >     would cause the system crash.
> >
> > Yes and dmaengine may fire a spurious irq..
> > >
> > > [2] vchan_cookie_complete() might being called at this point
> > >     and schedule the tasklet.
> > >     It might call uniphier_mdmac_desc_free() after
> > >     the reference disapperrs.
> > >
> > > Is this correct?
> >
> > Correct :)
> >
> > > Do you have recommendation
> > > for module removal guideline?
> >
> > Yes please free up or disable irq explictly, ensure pending irqs have
> > completed and then ensure all the tasklets are killed and in this order
> > for obvious reasons
> 
> Also, need to free up the left-over descriptor(s) right?
> Just killing the tasklets may result in memory leak.

Yes I am assuming you would have done so in terminate calls

> Please let know if the implementation in v4 is wrong.

Sure will do

-- 
~Vinod