Re: [PATCH v7 1/2] dmaengine: 8250_mtk_dma: add MediaTek uart DMA support

Long Cheng
2018-12-26T10:19:24Z

On Wed, 2018-12-26 at 17:28 +0800, Nicolas Boichat wrote:

......

> > > > > > +static int mtk_uart_apdma_device_pause(struct dma_chan *chan)
> > > > > > +{
> > > > > > + /* just for check caps pass */
> > > > > > + return 0;
> > > > > > +}
> > > > > > +
> > > > > > +static int mtk_uart_apdma_device_resume(struct dma_chan *chan)
> > > > > > +{
> > > > > > + /* just for check caps pass */
> > > > > > + return 0;
> > > > > > +}
> > >
> > > Why do you need these? Seems wrong to advertise device_pause/resume
> > > (and the caps) if we don't actually support that?
> > >
> >
> > in serial 8250_dma.c file, when request DMA, will calll
> > 'dma_get_slave_caps' to get the caps. and the will check caps.cmd_pause.
> > the pause is device_pause. our device can't support the functions. but
> > to check pass, need add the fake function. or you can give better
> > comments. thanks.
>
> Well, then I guess this is a hack... I'm not too familiar with
> 8250_dma.c, but I guess that if it requires pause/resume to be
> implemented, then we should implement them, not just stub them out...
>
> Is this something that can be implemented with 8250_mtk DMA?
>

the HW can't support it.

> Also, I don't see where you need resume, so maybe implementing pause is enough?
>

yes. pause is enough. for symmetry, add resume function.
anyway, the pause function need to keep.

> > > > > > +
> > > > > > +static void mtk_uart_apdma_free(struct mtk_uart_apdmadev *mtkd)
> > > > > > +{
> > > > > > + while (list_empty(&mtkd->ddev.channels) == 0) {
> > > > > > + struct mtk_chan *c = list_first_entry(&mtkd->ddev.channels,
> > > > > > + struct mtk_chan, vc.chan.device_node);
> > > > > > +
> > > > > > + list_del(&c->vc.chan.device_node);
> > > > > > + tasklet_kill(&c->vc.task);
> > > > > > + }
> > > > > > +}
> > > > > > +
> > > > > > +static const struct of_device_id mtk_uart_apdma_match[] = {
> > > > > > + { .compatible = "mediatek,mt6577-uart-dma", },
> > > > > > + { /* sentinel */ },
> > > > > > +};
> > > > > > +MODULE_DEVICE_TABLE(of, mtk_uart_apdma_match);
> > > > > > +
> > > > > > +static int mtk_uart_apdma_probe(struct platform_device *pdev)
> > > > > > +{
> > > > > > + struct mtk_uart_apdmadev *mtkd;
> > > > > > + struct resource *res;
> > > > > > + struct mtk_chan *c;
> > > > > > + unsigned int i;
> > > > > > + int rc;
> > > > > > +

......