linux-kernel - Re: [PATCH v5 2/2] media: i2c: add ov2735 image sensor driver

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Message-ID: <20250726094313.GD27425@pendragon.ideasonboard.com>
Date: Sat, 26 Jul 2025 12:43:13 +0300
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Hardevsinh Palaniya <hardevsinh.palaniya@...iconsignals.io>
Cc: Kieran Bingham <kieran.bingham@...asonboard.com>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	"sakari.ailus@...ux.intel.com" <sakari.ailus@...ux.intel.com>,
	Himanshu Bhavani <himanshu.bhavani@...iconsignals.io>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Hans Verkuil <hverkuil@...all.nl>,
	Ricardo Ribalda <ribalda@...omium.org>,
	Bryan O'Donoghue <bryan.odonoghue@...aro.org>,
	Hans de Goede <hansg@...nel.org>,
	André Apitzsch <git@...tzsch.eu>,
	Benjamin Mugnier <benjamin.mugnier@...s.st.com>,
	Matthias Fend <matthias.fend@...end.at>,
	Heimir Thor Sverrisson <heimir.sverrisson@...il.com>,
	Sylvain Petinot <sylvain.petinot@...s.st.com>,
	Dongcheng Yan <dongcheng.yan@...el.com>,
	Jingjing Xiong <jingjing.xiong@...el.com>,
	Arnd Bergmann <arnd@...db.de>,
	"linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 2/2] media: i2c: add ov2735 image sensor driver

On Sat, Jul 26, 2025 at 06:06:05AM +0000, Hardevsinh Palaniya wrote:
> > Quoting Hardevsinh Palaniya (2025-07-25 06:55:23)
> > <snip>
> > > > > +static int ov2735_page_access(struct ov2735 *ov2735,
> > > > > +�������������������������� u32 reg, void *val, int *err, bool is_read)
> > > > > +{
> > > > > +���� u8 page = (reg >> CCI_REG_PRIVATE_SHIFT) & 0xff;
> > > >
> > > > ' & 0xff' part is redundant.
> > > >
> > > > > +���� u32 addr = reg & ~CCI_REG_PRIVATE_MASK;
> > > > > +���� int ret = 0;
> > > >
> > > > How is this assignment being used?
> > > >
> > > > > +���� if (err && *err)
> > > > > +������������ return *err;
> > > > > +
> > > > > +���� mutex_lock(&ov2735->page_lock);
> > > > > +
> > > > > +���� /* Perform page access before read/write */
> > > > > +���� if (ov2735->current_page != page) {
> > > > > +������������ ret = cci_write(ov2735->cci, OV2735_REG_PAGE_SELECT, page, err);
> > > > > +������������ if (ret)
> > > > > +�������������������� goto err_mutex_unlock;
> > > > > +������������ ov2735->current_page = page;
> > > > > +���� }
> > > > > +
> > > > > +���� if (is_read)
> > > > > +������������ ret = cci_read(ov2735->cci, addr, (u64 *)val, err);
> > > > > +���� else
> > > > > +������������ ret = cci_write(ov2735->cci, addr, *(u64 *)val, err);
> > > >
> > > > Do you really need this castings?
> > >
> > > Do you really think this casting is unnecessary?
> > >
> > 
> > Yes? Well quite probably - I haven't checked myself yet but ..
> > 
> > 
> > > Please check the definitions of cci_read/write
> > >
> > > without this, we can't even build the driver.
> > 
> > How about ... changing the function prototype of ov2735_page_access ?
> 
> Of course, changing the function prototype would work.
> 
> My intention is to keep a single ov2735_page_access() function that can
> handle both read and write operations. The cci_read() function expects 
> a u64 *, whereas cci_write() expects a u64 value. To support both cases
> within one function, I’ve used a void *val and cast it appropriately 
> depending on the operation.
> 
> If we were to remove the casting, we would need to split this into two
> separate functions, one for read and one for write, even though the only 
> difference between them would be a single line. I’d prefer to avoid that
> redundancy and keep the code compact. 
> 
> Let me know if you see a better way to handle this without duplicating
> the logic. 

Move the cci_read() and cci_write() calls from the bottom of
ov2735_page_access() to ov2735_read() and ov2735_write() respectively.

-- 
Regards,

Laurent Pinchart