Re: [PATCH v2 3/3] dmaengine: tegra: Add support for dma-channel-mask

[Jon Hunter]

On 23/09/2022 11:17, Akhil R wrote:
> > On 19/09/2022 12:25, Akhil R wrote:
> > > Add support for dma-channel-mask so that only the specified channels
> > > are used. This helps to reserve some channels for the firmware.
> > >
> > > This was initially achieved by limiting the channel number to 31 in
> > > the driver and adjusting the register address to skip channel0 which
> > > was reserved for a firmware. Now, with this change, the driver can
> > > align more to the actual hardware which has 32 channels.
> > >
> > > Signed-off-by: Akhil R <akhilrajeev@xxxxxxxxxx>
> > > ---
> > >    drivers/dma/tegra186-gpc-dma.c | 37 +++++++++++++++++++++++++++-------
> > >    1 file changed, 30 insertions(+), 7 deletions(-)
> > >
> > > diff --git a/drivers/dma/tegra186-gpc-dma.c b/drivers/dma/tegra186-gpc-
> > dma.c
> > > index fa9bda4a2bc6..1d1180db6d4e 100644
> > > --- a/drivers/dma/tegra186-gpc-dma.c
> > > +++ b/drivers/dma/tegra186-gpc-dma.c
> > > @@ -161,7 +161,10 @@
> > >    #define TEGRA_GPCDMA_BURST_COMPLETION_TIMEOUT	5000 /* 5
> > msec */
> > >    /* Channel base address offset from GPCDMA base address */
> > > -#define TEGRA_GPCDMA_CHANNEL_BASE_ADD_OFFSET	0x20000
> > > +#define TEGRA_GPCDMA_CHANNEL_BASE_ADDR_OFFSET	0x10000
> >
> > Why did this value change? There is no mention in the commit message. If
> > this was incorrect before, then this needs to be a separate patch and
> > tagged with the appropriate fixes tag so that this can be picked up for
> > stable.
> This is mentioned in the commit message.
>
> "... and adjusting the register address to skip channel0 ..."
>
> Probably it is not very clear that it directs to this change. Shall I update the
> commit message to have a clearer context?

Ah OK. I was wondering how this worked with 'channel_reg_size' but 
looking closer I see channel_reg_size is always SZ_64K. I wonder why we 
even bother having this parameter and don't use SZ_64K directly?

Anyway, for now this is fine.

Jon

--
nvpublic