linux-kernel - Re: [PATCH v3 4/6] bus: stm32_sys_bus: add support for STM32MP15 and STM32MP13 system bus

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Date:   Wed, 8 Feb 2023 19:08:33 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Gatien CHEVALLIER <gatien.chevallier@...s.st.com>
Cc:     <Oleksii_Moisieiev@...m.com>, <gregkh@...uxfoundation.org>,
        <herbert@...dor.apana.org.au>, <davem@...emloft.net>,
        <robh+dt@...nel.org>, <krzysztof.kozlowski+dt@...aro.org>,
        <alexandre.torgue@...s.st.com>, <vkoul@...nel.org>,
        <olivier.moysan@...s.st.com>, <arnaud.pouliquen@...s.st.com>,
        <mchehab@...nel.org>, <fabrice.gasnier@...s.st.com>,
        <ulf.hansson@...aro.org>, <edumazet@...gle.com>, <kuba@...nel.org>,
        <pabeni@...hat.com>, <linux-crypto@...r.kernel.org>,
        <devicetree@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <dmaengine@...r.kernel.org>,
        <linux-i2c@...r.kernel.org>, <linux-iio@...r.kernel.org>,
        <alsa-devel@...a-project.org>, <linux-media@...r.kernel.org>,
        <linux-mmc@...r.kernel.org>, <netdev@...r.kernel.org>,
        <linux-phy@...ts.infradead.org>, <linux-serial@...r.kernel.org>,
        <linux-spi@...r.kernel.org>, <linux-usb@...r.kernel.org>,
        Loic PALLARDY <loic.pallardy@...com>
Subject: Re: [PATCH v3 4/6] bus: stm32_sys_bus: add support for STM32MP15
 and STM32MP13 system bus

On Tue, 7 Feb 2023 15:12:23 +0100
Gatien CHEVALLIER <gatien.chevallier@...s.st.com> wrote:

> Hi Jonathan,
> 
> On 1/28/23 17:12, Jonathan Cameron wrote:
> > On Fri, 27 Jan 2023 17:40:38 +0100
> > Gatien Chevallier <gatien.chevallier@...s.st.com> wrote:
> >   
> >> This driver is checking the access rights of the different
> >> peripherals connected to the system bus. If access is denied,
> >> the associated device tree node is skipped so the platform bus
> >> does not probe it.
> >>
> >> Signed-off-by: Gatien Chevallier <gatien.chevallier@...s.st.com>
> >> Signed-off-by: Loic PALLARDY <loic.pallardy@...com>  
> > 
> > Hi Gatien,
> > 
> > A few comments inline,
> > 
> > Thanks,
> > 
> > Jonathan
> >   
> >> diff --git a/drivers/bus/stm32_sys_bus.c b/drivers/bus/stm32_sys_bus.c
> >> new file mode 100644
> >> index 000000000000..c12926466bae
> >> --- /dev/null
> >> +++ b/drivers/bus/stm32_sys_bus.c
> >> @@ -0,0 +1,168 @@
> >> +// SPDX-License-Identifier: GPL-2.0
> >> +/*
> >> + * Copyright (C) 2023, STMicroelectronics - All Rights Reserved
> >> + */
> >> +
> >> +#include <linux/bitfield.h>
> >> +#include <linux/bits.h>
> >> +#include <linux/device.h>
> >> +#include <linux/err.h>
> >> +#include <linux/io.h>
> >> +#include <linux/init.h>
> >> +#include <linux/kernel.h>
> >> +#include <linux/module.h>
> >> +#include <linux/of.h>
> >> +#include <linux/of_platform.h>
> >> +#include <linux/platform_device.h>
> >> +
> >> +/* ETZPC peripheral as firewall bus */
> >> +/* ETZPC registers */
> >> +#define ETZPC_DECPROT			0x10
> >> +
> >> +/* ETZPC miscellaneous */
> >> +#define ETZPC_PROT_MASK			GENMASK(1, 0)
> >> +#define ETZPC_PROT_A7NS			0x3
> >> +#define ETZPC_DECPROT_SHIFT		1  
> > 
> > This define makes the code harder to read.  What we care about is
> > the number of bits in the register divided by number of entries.
> > (which is 2) hence the shift by 1. See below for more on this.
> > 
> >   
> >> +
> >> +#define IDS_PER_DECPROT_REGS		16  
> >   
> >> +#define STM32MP15_ETZPC_ENTRIES		96
> >> +#define STM32MP13_ETZPC_ENTRIES		64  
> > 
> > These defines just make the code harder to check.
> > They aren't magic numbers, but rather just telling us how many
> > entries there are, so I would just put them in the structures directly.
> > Their use make it clear what they are without needing to give them a name.
> >   
> 
> Honestly, I'd rather read the hardware configuration registers to get 
> this information instead of differentiating MP13/15. Would you agree on 
> that?

Sure, if they are discoverable even better.