Re: [PATCH v6 08/10] misc: rp1: RaspberryPi RP1 misc driver

[Andrea della Porta <andrea.porta@suse.com>]

Hi Greg,

On 09:48 Tue 21 Jan     , Greg Kroah-Hartman wrote:
> On Tue, Jan 21, 2025 at 09:43:37AM +0100, Andrea della Porta wrote:
> > Hi Greg,
> > 
> > On 12:47 Fri 17 Jan     , Greg Kroah-Hartman wrote:
> > > On Mon, Jan 13, 2025 at 03:58:07PM +0100, Andrea della Porta wrote:
> > > > The RaspberryPi RP1 is a PCI multi function device containing
> > > > peripherals ranging from Ethernet to USB controller, I2C, SPI
> > > > and others.
> > > > 
> > > > Implement a bare minimum driver to operate the RP1, leveraging
> > > > actual OF based driver implementations for the on-board peripherals
> > > > by loading a devicetree overlay during driver probe.
> > > > 
> > > > The peripherals are accessed by mapping MMIO registers starting
> > > > from PCI BAR1 region.
> > > > 
> > > > With the overlay approach we can achieve more generic and agnostic
> > > > approach to managing this chipset, being that it is a PCI endpoint
> > > > and could possibly be reused in other hw implementations. The
> > > > presented approach is also used by Bootlin's Microchip LAN966x
> > > > patchset (see link) as well, for a similar chipset.
> > > > 
> > > > For reasons why this driver is contained in drivers/misc, please
> > > > check the links.
> > > 
> > > Links aren't always around all the time, please document it here why
> > > this is needed, and then links can "add to" that summary.
> > 
> > Ack.
> > 
> > > 
> > > > This driver is heavily based on downstream code from RaspberryPi
> > > > Foundation, and the original author is Phil Elwell.
> > > > 
> > > > Link: https://datasheets.raspberrypi.com/rp1/rp1-peripherals.pdf
> > 
> > ...
> > 
> > > > diff --git a/drivers/misc/rp1/rp1_pci.c b/drivers/misc/rp1/rp1_pci.c
> > > > new file mode 100644
> > > > index 000000000000..3e8ba3fa7fd5
> > > > --- /dev/null
> > > > +++ b/drivers/misc/rp1/rp1_pci.c
> > > > @@ -0,0 +1,305 @@
> > > > +// SPDX-License-Identifier: GPL-2.0
> > > > +/*
> > > > + * Copyright (c) 2018-24 Raspberry Pi Ltd.
> > > > + * All rights reserved.
> > > > + */
> > > > +
> > > > +#include <linux/err.h>
> > > > +#include <linux/interrupt.h>
> > > > +#include <linux/irq.h>
> > > > +#include <linux/irqchip/chained_irq.h>
> > > > +#include <linux/irqdomain.h>
> > > > +#include <linux/module.h>
> > > > +#include <linux/msi.h>
> > > > +#include <linux/of_platform.h>
> > > > +#include <linux/pci.h>
> > > > +#include <linux/platform_device.h>
> > > > +
> > > > +#include "rp1_pci.h"
> > > 
> > > Why does a self-contained .c file need a .h file?  Please put it all in
> > > here.
> > 
> > I agree with you. Indeed, the very first version of this patch had the header
> > file placed inside the .c, but I received concerns about it and some advice to
> > do it differently, as you can see here:
> > https://lore.kernel.org/all/ZtWDpaqUG9d9yPPf@apocalypse/
> > so I've changed it accordingly in V2. So right now I'm not sure what the
> > acceptable behaviour should be ...
> 
> It's a pretty simple rule:
> 	Only use a .h file if multiple .c files need to see the symbol.
> 
> So no .h file is needed here.

Perfect, I'll revert back that two lines to V1 then. Please be aware
though that this will trigger the following checkpatch warning:

WARNING: externs should be avoided in .c files

> 
> > > > +struct rp1_dev {
> > > > +	struct pci_dev *pdev;
> > > > +	struct irq_domain *domain;
> > > > +	struct irq_data *pcie_irqds[64];
> > > > +	void __iomem *bar1;
> > > > +	int ovcs_id;	/* overlay changeset id */
> > > > +	bool level_triggered_irq[RP1_INT_END];
> > > > +};
> > > > +
> > > > +static void msix_cfg_set(struct rp1_dev *rp1, unsigned int hwirq, u32 value)
> > > > +{
> > > > +	iowrite32(value, rp1->bar1 + RP1_PCIE_APBS_BASE + REG_SET + MSIX_CFG(hwirq));
> > > 
> > > Do your writes need a read to flush them properly?  Or can they handle
> > > this automatically?
> > >
> > 
> > I had some thoughts with RaspberryPi foundation folks to double check it, and it
> > seems that there should be no need to readback the value (unless we want to go
> > really paranoid), so I would avoid that since in case of level handled interrupt
> > we would end up reading the register on every triggering interrupts.
> 
> Ok, if it passes testing, that's fine, hopefully it works properly, but
> if not, you now have a trail to go and fix it in the future :)

Sure :)

Many thanks,
Andrea

> 
> thanks,
> 
> greg k-h