Re: [PATCH v6 1/8] drm: bridge: dw_mipi_dsi: add initial regmap infrastructure

[Adrian Ratiu]

On Thu, 16 Apr 2020, Enric Balletbo Serra <eballetbo@xxxxxxxxx> 
wrote:
> Hi Adrian, 
>
> [snip] 
>
> > >> 
> > >> +static void dw_mipi_dsi_get_hw_version(struct dw_mipi_dsi 
> > >> *dsi) +{ +       regmap_read(dsi->regs, DSI_VERSION, 
> > >> &dsi->hw_version); +       dsi->hw_version &= VERSION; + if 
> > >> (!dsi->hw_version) +               dev_err(dsi->dev, "Failed 
> > >> to read DSI hw version register\n"); 
> > > 
> > > Is this an error that should be ignored? If you can't get the 
> > > HW version, probably, there is something wrong with your 
> > > hardware so, don't you need to return an error? 
> > > 
> >
> > After thinking a bit more about it, that error should be a 
> > warning. 
> >
> > I added it because in some cases (for eg. if the peripheral 
> > clock is disabled) the reads can return 0 which is obviously an 
> > invalid version and the bridge will error in the next step when 
> > not finding a layout. 
>
> If you'll error anyway, why wait? IIUC at this point the clock 
> *must* be enabled, and if not, something is wrong with the 
> driver, I don't see any advantage on delay the error. do you 
> have a use case where this is called and peripheral clock 
> disabled? 

There should be no real use-case (maybe malfunctioning HW), and we 
could error out here to catch driver bugs ASAP, so I'll go this 
route then :)

Thank you, much appreciated!

> > So I'll make this a warning in v7 and explicitely mention that
> > reads version == 0 can be caused by a disabled pclk.
>
> -- Enric
>
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